Registration when molding gloves?

Classic problem, but I can't seem to find anything that addresses it.

I'm trying to sculpt and mold flexible gloves for a Halloween costume. Lifecasting my hand and sculpting over it is no problem. The problem I run into is if this is true glove, with no clear space on either side of my hand, I don't know how to register the plaster lifecast inside of the (presumably) 2-part mold. The way I picture it. if I do nothing it will sag towards one side or the other and I'll have a thin section (or worse). I supposed I could also just slush cast it, but I'd rather have a tighter fit.

I guess the correct method would be to register the base of the mold some where further up my the lifecast of my arm where the glove isn't, then mold it vertically? I'm sure I've seen examples of a way to do this before, but I can't find everything, and all the google results tell me about glove molding, not molding.... a glove.

Glove? Hollow? Wearable?

OK, from your description, You would like the cast of your arm to register (locate) in the mold @ the thickness of the sculpted glove, so that the casting will be hollow and your hand fits in there?

What you are trying to describe, is a Core-Mold. That is pretty complicated to describe by typing away, but can be done. Since this is a Halloween costume, could you try pouring the rubber into the mold, and then pouring it out? This gives you a layer of rubber, and depending on the type of rubber, you may need to do multiple coats. The advantage is that you just mold the sculpt, and don't need to worry about the core registering.