W4N DB split process

I am curious who has performed a DB split after the fact and is using the loab-balancer in the configuration? I have perfromed the split several times and I am trying to shorten the process by purging the unwanted data in the split databases without having to wait for the retention policy to kick in. In my splits I have adjusted the retention policy to 1 day and that didnt help.

In my example I have a DB that is 500GB and I have  physical server with 1TB drive. I am unable to add storage. I need to split into 4 DBs. I take my 500GB copy and move it to a location where I have enough space (3TB) and I perform my deletes to the reference data. I am left with 4-500GB DBs, which will not fit back on my original 1TB server, however it will after the "purge" of the unwanted data happens in 30 days(according to the documented retention policy).

How do i get the 4 DBs to shrink to fit?