During Replenish Report, there is an option to replenish from a source warehouse to a target warehouse internally. However it forces the Replenish records to be filtered by existing vendor, which will fail a simple transfer of internally produced goods.
Simple small patch attached.
. It won't impact the process that filters by Vendor, present in T_Replenish in the end.
Of course the user has to assign a Vendor to process the resulting Movement document, but at least s/he can produce the draft report first.