Complicated depth problem

heres basicly my problem , im attaching movieclips to _root using a string called depth which increases by 1 everytime a movieclip is added . so ive got the entire 101 - 200 depth range for movieclips 201 - 301 is for my ui and so forth .

So everything is working nicly but theyres just one problem , i have a drager movieclip and when its clicked i want to set its depth to 199 or something.like getnexthighestdepth but i have to keep it inside the 100-200 range, i cant usea container movieclip either because thatwillmess up the window manager

any ideas ?