Hey Jam,
i did the same thing. i have an omi v2 so it's fine for me, but i bought one for a buddy and now i realize i can't use it w/ out the other bottom. I am wondering if maybe THC will be willing to sell or trade out some bottom caps. i hope so, 'cuz if not i'm out of pocket. the mini omi should really be a unit, imho.
that's a bummer, i had a little trouble, but got it on and both are running fully functional (i also got two of the hvd's so i'd have two unreg tops and the extra batts.)
EDiT - well, i spoke to soon, so i tried to put my silver HVD on my omi. it threaded a few threads, then stuck a little. i figured it was just new machining and that a little push would clear the thread. WRONG. no movement, then i tried unscrewing it and it's stuck. i grab a pair of pliers and a jar wrench and try to unscrew them. i ended up shredding the fuck out of my new chrome top, marking up my old v2 tube and now both are completely fucked and jammed together. am really upset and trying to calm down. walking away from the problem for now.