seems like you would need to configure TextMate’s compiler search paths … probably the linker search paths as well. Really not sure if TextMate supports all the compile options you would need to get OF to compile and link everything it needs. You might have some luck in adding the OF paths to the environment variables section in TextMate’s advanced preferences tab.
If you do need more advanced gcc-specific options, I might suggest (which may or may not work) creating a shell alias for gcc that has the extra options and then setting that as your compiler in TextMate. I think a first step with this approach would be to get it compiling properly from your command line so you know exactly which options you need. I think there might be a way to get XCode to spit the command out for you from within one of the example projects.
Just wondering … any reason you don’t want to use XCode? I love using TextMate for web stuff (it really is a great little IDE), but I use XCode for all my OF stuff, because I don’t want to go through the trouble of making the project template for a different IDE. Also keeping in mind that some add-ons and libraries require certain frameworks which XCode can add in with a couple clicks - again I don’t know about TextMate’s support for these.