Constant trimming isn't exactly good for plants, so if that's what the result of adding Co2 is then you might want to rethink it. I have pressurized CO2 on my 5.5, but my lighting is low enough that I'm not particularly having problems from it.
trimming depends on the plants. Many stem plants LOVE to be trimmed, that is one way to get the very thick dense bushes found in many aquariums. here is a trimming journal off of another forum. There are some stems taht do not like to be trimmed, but for the most part it encourages growth, lotus's become more dense, stems throw out side shoots, swords throw up more leaves ect.
The fluval miniCo2 kit doesn't dose with bubbles. It's basically an upside-down reservoir that you fill with co2 once or twice a day and it slowly mixes into the water over the course of an hour or so. imagine like a small bowl that hovers upside-down in ur tank, then u put a co2 gas pocket under the bowl periodically and that pocket dissipates into the water flowing by.
there are two fluval systems out there, there is the bell type that comes with the flora, and has a smaller cartridge, and then there is the 88g kit that comes with a ceramic diffuser, and regulator.
the only problems with these two systems is the cost. they get expensive really quick due to the cost of the cartridges.
to the OP, in the DIY part of the forum, you will find a link near the top to a DIY paintball system. The needle valve is really finicky though. I personally use this : http://www.thatpetplace.com/pet/group/4531/product.web
the needle valve is not the greatest, but it works well. it turns off at night when attached to a timer, and does not need refilled that often (about every 6 months or so on my 7.8gal fluval flora) the refills are cheap (3.50 at sports authority) and you can get them filled at most sports equipment stores.
Co2 is never a bad thing, even for low light plants. Carbon is essential for proper plant growth. if your light is lower, your plants will grow slower, more light, more demand for co2 and faster growth.