I need to do the same sort of things wiht some of my imperial guard. I have done it before but not without damaging the model so yeah it can be quite difficult.
I'm going to try Lazarus tactic as I'm pretty heavy with glue and I'd end up snapping half their foot off if I tried to wedge.
I'll update the post when I've got some ironhalo bases to transfer my marines onto, it's no trouble with metal models of course, you can simply snap them off the bases

no damage reported doing this so far.