Virtual Sub Pages

What I want to do:

Create a page that has more than 100 sub pages. I don’t want to create all this sub pages using wp-admin by hand.

If the page that has all the children is located in myblog.de/mypage/
all requests like myblog.de/mypage/somesubpage/
should be handled in the special template that is assigned to ‘mypage’. This template loads the contents from a non-wp database table.

So far I can only handle myblog.de/mypage/?sub=subpage using $_SERVER[‘REQUEST_URI’]. If I use mod_rewrite like
RewriteRule ^mypage/([\w,=;\-]+)$ mypage/?sub=$1
I still get a 404. I think this is because mod_rewrite doesn’t modify $_SERVER[‘REQUEST_URI’]. So wp still gets a request like ‘myblog.de/mypage/somesubpage/’ and serves only a 404 page. (I dumped $_SERVER[‘REQUEST_URI’] on my 404 page)

I had a quick look at rewrite.php (add_rewrite_rule) but I’m not sure how to use it and if it’s the right thing to use.