The geometry of the tubes might make a FD impossible. email Swift to see if they have any advice, they sell custom bikes so they may have mounted some themselves.
SRAM duel drive rear hub, or the (I forget the brand) internally geared BB might solve your problem for more $$ and less time.
If you are looking for a lower gear, the shimano mega range thread on freewheel&cluster has treated me well. The mega range might be the easiest upgrade for you. Infact I ditched all but one chainring (44t), although I mostly use my bike for commuting and riding on relatively flat terrain, I have used it for 'touring' day trips on hilly and steep rides. This would not work for real touring ie hauling alot of gear (tents, extra clothes, full tool kit, sat phone, ...).
2000 Montague CX, I do not recommend it, but still ride it.
Strida 3, I recommend it for rides < 10mi wo steep hills.
2006 Rowbike 720 Sport, I recommend it as an exercise bike.
1996 Birdy, Recommend.
Wieleder CARiBIKE (folding), decent frame.