Almost all thermostats have a FAN switch, that can be set to ON or AUTO. In the AUTO position, the blower comes on when the furnace needs it (during heat/cool calls). In the ON position, the blower will always be on. This is usually controlled by the G terminal on the furnace and thermostat.
I'm not sure exactly what you're trying to do, so I'll cover a couple different setups
Blower on when you want
For this situation, simply connect the G terminal on the thermostat to the G terminal in the furnace. When you want the blower on, set the thermostats FAN setting to ON.
Blower on when house is too warm
If you want the blower to come on when the temperature in the house raises above a set temperature, you'll simply connect the Y terminal of the thermostat to the G terminal in the furnace. This way whenever the thermostat calls for cool, the blower fan will come on.
Depending on the furnace, you may be able to connect the Y terminal on the thermostat to the Y terminal in the furnace, and simply not connect any control wires from the furnace to the A/C unit. Most furnaces activate the blower after a predetermined (possibly programmable) delay, when the thermostat calls for cool.
Blower speed (Multi-speed blower)
Blower speed may vary based on the different functions. For example, heat might be medium low, fan might be low, while cool may be high speed. So you'll want to take that into consideration as well.
Without more information about your specific equipment, and what exactly you're trying to accomplish. It's difficult to provide more accurate, specific information.
I suggest a swamp cooler - or as Home Depot calls them online 'Portable Evaporative Cooler.'
The big ones (which do come with wheels), a seem to do well in the reviews. There are many negative ones, but those seem mostly from people who do not understand what the product does. The are listed under the Air Conditioning heading, and talk about how much cooler they will make the room.
But you will not sell many with a slogan of 'These things toss water in the air, hope it sticks to you, and when the hot air, with no humidity from outside hits you, it will evaporate off your skin, and you will feel cooler'.
However, if your goal is to have humidity - even most of the negative reviews will sound good to you.
Best Answer
The problem is that your air conditioner is probably over sized or the fan speed is set too high. An air conditioners primary function is to remove moisture from the air. To big of an air conditioner and it drops the temperature too fast and can't pull down the relative humidity. If the fan speed is too high then the interior coil doesn't get cool enough to cause water to condense and drip into the drain. There are a few ways to make the air conditioner do its primary job of humidity removal work better. The simplest is lowering the fan speed. This link explains some tactics with a little detail. Air conditioning is tricky and it requires many measurements with specialized tools. It's not really a DIYer job but, with enough acquired knowledge anyone can understand it. Lots of installers and service techs don't actually know what they are doing. They often set the fan to the highest available speed, install the largest equipment possible, charge the system with the beer can cold method and generally accept that if it's blowing cold air it's perfect. That is not the case. Get a good, reputable service tech over and explain the issue. You don't need a dehumidifier, you need to set up the one you have. A good tech will have your house cool and dry in no time.
I'm from Toronto, we get a dry -40°F to a very sticky 110°F. If we can get by without dehumidifiers here, you can in Pennsylvania.