Pre-mortal existence (other than Christ of course) makes a good backdrop for a novel, movie or television script. And it is LDS theology (and a minority view in Judaism and Islam.)
But it is not Scriptural:
Actually this supports my speculation..
The mechanics of the forming is not mentioned..
What is,is, and what ain't, ain't.. Spectulation is fun..
I think I will not be judged on how accurate my spectulations are..
There may be some Mormons in heaven.. I say God bless them..
We are no doubt not judged on how smart we are..
If we were, many smart alecks will not be there..
You know like Peter, Thomas.. etc..