Because I can't read the url that is causing you problems very well, I am not sure if I understand your question correctly.
Although I guess your problem is that you want to have it the 'old school dynamic way' and the 'look like static way' as well.
If so, you can first look for a questionmark in the $_SERVER['PATH_INFO'] - your re-written url will not have that.
index.php?bla=1&id=2 (has questionmark)
index.php/bla/1/id/2 (does not have questionmark)
If not so, don't mess with the $_GET array, because all the info you need is in there.
I hope this solves your problem
cheers,
Tobias