Why sp much fuss about TM2 when there is a trivial workaround?
1) open /Applications/TextMate.app/Contents/Resources/Info.plist
2) change CFBundleShortVersionString = "1.5.9" to CFBundleShortVersionString = "2.0.1" (remember: never upgrade to 2.0.0, wait for the bugs to be ironed out)
3) do the same for CFBundleGetInfoString = "1.5.9 (1589)"
You might want to change also the 1589 version number, but I think that would be overkill.
Enjoy! Piero