General: Can you replace waterbottle mounts in your frame?

I'm not sure what they're called. It's the little aluminum pressed in pieces that go into your aluminum frame for bottle cage bolts, the same ones that also get put into the sides of seat stays and fork legs for rack mounts. If one of them were to come loose, is there a way to pull it out, and put a new one in, or would I do best to just leave it how it is so I don't end up with a hole in my frame?

I bought a used frame, and it has one of those pieces pressed up on the inside of the seat stays where the brake bridge would be. It's there so you can drill a hole in your fender and just bolt it straight into the bottom of the brake bridge instead of messing with those clipped on plastic pieces. (It's basically this, only what would be put into an aluminum frame, instead of brazed into steel, but just so you have an idea of what I'm talking about.... http://www.dominguezcycles.com/images/gallery/12/lres/013.jpg ) I noticed there was a piece of a broken bolt still stuck in there, so I drilled a hole in it and tried to pull it out with a stripped screw remover. I eventually just ended up pulling the whole piece loose. It's not shaking around, but it'll spin if I try to twist the bolt out. It'd be nice to pull it out and stick a new one in, but I wasn't sure if trying would most likely leave me with a big whole in the frame, and if that's the case, I'll just stick to the zip ties.

You should be able to replace that. Often your LBS will have all shapes and sizes of those things laying around. The shop I used to work at certainly did. Just a matter of finding the right fit.
So I'm confused a bit about that bridge though. If you were to run a rear brake and a fender through the other hole it looks like it'd be an impossible setup. Am I just seeing things wrong?

Yeah, that was just an example I found on google anyway. My frame has cantilever mounts, The seat stays are pretty much just one long tube bent in a U shape, with a bar welded to the top, here's a picture of the back end.... http://velospace.org/files/cdalecyclocross02.JPG so mine doesn't have a way of messing with the brakes. Maybe I'll try giving Cannondale a call tomorrow. Although, now that they're laying off 2/3 of their company to ship the jobs to Taiwan, my faith in their customer service is going downhill.