You can use a block connector (you can bridge it - on one side loop a a wire into each terminal to make it like one big connector)
or You can use a twist connector
I was searching for something like this. But an insulated version- i found something in china but the problem is it will never be approved to use that on internal circuits due to high risk of electrical shock. These are used inside distribution boards only - and can only be installed by qualified electricians.
First, everything about the Sonoff stinks like cheap Cheese, so good bet it is not UL listed. RoHS and CE is nothing, and UL/CSA listings are often forged by those offshore manufacturers.
Mains electrical is serious business, and the stuff is already very cheap - $20 for a proper smart switch for instance. The only reason that price seems high is you have found this thing that is cheaper in several ways, most bad. Who cares? There will always be a cheaper piece-o-junk out there. Your time is valuable too.
In NEC jurisdictions you cannot install things not approved by your local inspector, who does not run his own testing lab, but simply gets a list of approved appliances from UL or similar entity. NEC 110.
You cannot mount outside a junction box
An electrical device cannot be mounted outside a junction box as you plan, unless the labeling or instructions tell you to install it that way - the labeling and instructions are part of the UL listing, the listing is contingent on it being installed properly, and it is illegal to install it contrary to those instructions (NEC 110.3).
Parallel switches in your plan are semi-OK
The fact that the Sonoff has netural coming in is simply due to the fact that it is a powered device and needs neutral for its own power. Whether it is switching neutral, I cannot guess: It may be possible to bypass its neutral output and serve the neutral from the other side - that depends (again) on the UL approved labeling and instructions on the device.
If that's the case, then having both the smart switch and the plain switch feed the light should be fine. The key rule is that in any cable, currents must be equal - cancel each other out. That is to avoid eddy-current heating.
Low voltage remote switches are even better
If Deepesh Golani's method of accessing the internal switch works, and (again) is supported by UL approved labeling or instructions, that is an even better way since it does not involve significant currents. If that power is low voltage, you would escape the requirement to use Class 1 wiring techniques, and could run remote switches with thermostat wire for instance.
Best Answer
This has great potential to become a hokey fix-up DIY bodge, but try not to be tempted into cutting all the corners.
BTW, you said it's "only pulling 24v" which is incorrect. It's pulling 240v, but only 0.2A
That's actually less than half the power consumed by a 60w light bulb, so even if your ring is running a chandelier in the hall too, it's unlikely to be anywhere near maximum capacity, which is 5A.
Right. That settled, onto the bodge…
Is it to building regs? No.
Is it actually going to hurt anything if you do it properly? No.
Would I do it? Yes.
You're going to need to wire it in parallel above the drop to the light switch unless you only want it to work when the light's on*. Don't try to wire it in above the light itself. That's a no-no.
Late edit.
I feel I ought to clarify this, reading back.
The ring main runs round from light to light, not from switch to switch, so directly above the fitting you can get to it - but it's in the porch, so it's not weather-proof enough for a cheap switch-mode power supply. You have to find another segment of the ring indoors to wire from (not the drop to the switch, that's not in the ring.)
End of edit now read on…
Do not place it outdoors, even in a porch, no matter what you box it in. That it has air-vents tells you it needs some airflow, so you cannot box it up tight enough to be placed outside the main building. It will get just enough airflow placed in the ceiling so long as it's placed in free-space.
To get it closer to building regs, if not absolutely to spec, you really ought to put an old-style 5A socket on a joist in the ceiling space & plug it to that - that way anyone who finds the socket in the distant future won't expect it to be on the ring main at 13A. That would also allow you to correctly earth the socket. At a push, put a 13A socket in & label it 5A Lighting. Use correct boxes at any junction you need to make - no insulating tape, no free-floating terminal block & no solder, thank you very much.
Of course, by the time you get up into the ceiling space, you might find you're close enough to a regular ring main to just run a spur off that, legit, kosher & above-board.
If there was any part of the simple terminology I've used in this answer that you don't understand, get an electrician ;)
*That's kind of a joke… don't do that.