I'm pretty sure you do need C02 in order to seal the keg and would say using C02 bulbs to seal and then dispense a bit counter productive (not to mention very expensive, unless you really don't have room for a small gass bottle).
Also, I've seen some American videos on YouTube of people doing something similar by having the keg on a kind of stillage, top end lower than the bottom, swapping the short dip tube to the liquid out post and using the kind of tap used for inline drinking water filters as a beer engine.
Bag in a box is probably a better idea if you can get over the fact the bags are single use. Or polypins. There are some people out there who've had great success using them. And you don't have to spend money on taps etc, though I have used them with a hand pull before.