Well, with a lathe and milling machine, etc, why not make your own mount
A HEQ5 is a little too much to be lugging about, that's why I suggested the smaller mounts. The iOptron mount isn't all that much larger than the polarie and tripod itself. But the polarie has less "fiddly bits" to lug about, like hand controller etc.
You may find that adding to the polarie and/or modding it might overtax the tracker completely and render it useless for what you want. To be able to drift align it, you're going to have to be able to correct in both axes and these trackers just aren't designed to do so. The only way to correct in Dec would be to have a dec motor/drive in the tripod head and sync it with the RA motor in the tracker.