Only room for one cage...

[Mr. Bloom]

Dor-a, there are cages that attach with velcro...they're not expensive and can be easily attached and removed.

I use one. It's adequate and does the trick in hot weather when you must hydrate more.

[OakLeaf]

zip ties? sure they're ugly, but most people use them to attach cadence sensors, computer cables, etc.

[Zen]

It ain't pretty but it does the job-
http://www.twofishunlimited.com/bike.html

[Mr. Bloom]

That's the one I have. As long as the velcro is tight, it's just fine.

[Eden]

Hose clamps - I used them to put a bottle on my old Marin, as it also had no bolts on the seat tube.

[VeloVT]

I was going to say hose clamps too. They are **slightly** less ugly than zip ties (in my opinion, anyway). They work quite well too.

[uforgot]

I've used the Minoura water bottle cage adapter and it works really well. The pics don't show it, but you can put it on the tube where your bottle normally goes also. That's what I did with my mixte.