[RPG] How to make the paladin alive again without his whole body

NO.

Quote from Pathfinder SRD:

Whenever the paladin uses lay on hands to heal damage to one target, the target also receives the additional effects from all of the mercies possessed by the paladin.

Using lay on hands to channel energy is clearly not the case.

As TechImp points out, one increase can be gained via (permanencied) enlarge person. This leads to the problem that the spell states:

Multiple magical effects that increase size do not stack.

Meaning we now need to find a second, nonmagical effect to increase in size. In this case, we will look for abilities that are neither spells nor spell-like abilities.

Synthesist Summoner (8th or 13th)

Fused Eidolon
A synthesist summons the essence of a powerful outsider to meld with his own being. The synthesist wears the eidolon like translucent, living armor. The eidolon mimics all of the synthesist’s movements, and the synthesist perceives through the eidolon’s senses and speaks through its voice, as the two are now one creature.

This allows you to summon your own personal translucent Gundam! (Remember, the Eidolon looks like the Summoner wants it to look like) Also, Fused Eidolon has no type (Sp, Ex, Su), so we can assume that it is non-magical (by RAW).

Take the Large Evolution and combine it with enlarge person to become huge.

Large
An eidolon grows in size, becoming Large. [...] The summoner must be at least 8th level before selecting this evolution. [...]
If 6 additional evolution points are spent, the eidolon instead becomes Huge. [...] The summoner must be at least 13th level before selecting this option.

Or just become huge directly at 13th level, with the option for Gargantuan...

This works as long as your Eidolon is alive, which is as long as you are conscious, due to Life Link.

Gifted Blade or Psychic Warrior (7th)

You can also use the 1st level psionic power Expansion

This power causes instant growth, doubling your height, length, and width and multiplying your weight by 8. This increase changes your size category to the next larger one. [...]
If you spend 6 additional power points, this power increases your size by two size categories instead of one. [...]

You need to have a Manifester level of 7th to use 7 power points on one ability. Note that you can not combine this with any other method, since the power states:

Multiple effects that increase size do not stack, which means (among other things) that you can’t use a second manifestation of this power to further expand yourself.

The duration is the same as for enlarge person, 1min/lvl.