I'm definitely not an expert, but I bet you could take a hedge trimmer to them and whack them back to whatever dimension you wanted without too much harm. Roses are pretty tough; the minis do not seem to be an exception. Again, I offer the caveat that I do not have the mini experience that most here have. I've read studies of pruning "regular" roses using varying methods and in some cases, the "chain saw" method produced the most roses. Go figure. My landlord used to take a pair of electric hedge trimmers and just butcher the hedge in front of my apartment. It always drove me crazy (looked so ugly for a while) but they roses always bounced back thick as ever.

http://www.leevalley.com/garden/page.aspx?c=2&cat=2,42706,40719&p=10250
Now, the site says they don't have it now, but it might be the kind of thing you can ask for at a good nursery.