If you can get a GS bad clone there, you can drop it off at daycare, and pick it up again to transform the GS bad clone into a 000.
From there, you can put it at the top of your list to cloak your 5 other Pokemon, and put a 7th in your party. From there, you can drop off the 000, then deposit the things that you want to transform (and are equipped with the appropriate attacks) into a box 1 by 1. After that, take back the 000 (which will transform into 255, incidentally). Now take out the monster(s) that were poised for transformation (for example, the 2nd monster you deposited was to be Celebi, it'd need a Beat Up attack in the 1st position. If the 3rd monster you deposited was to be Celebi, it'd need a Beat Up attack in the 2nd position. The 1st monster can't generally become Celebi, since it would be required to hold HM 09, something that'd you have to glitch to get first).
The next step is to leave the monster poised to transform with the daycare man (I guess lady would work too?). If you go outside, you should see that it has transformed. Go back in, and take it back. You should now have your new monster.