Avoiding Outlook OST regeneration

Hello all-

We are performing an intra-forest domain consolidation (child into parent). Customer is currently on Office 365 which resides on the target. Pre-migration, users would log into their respective child domains and then into the parent for email. 

Our process is to merge their source account into the target. Process is fine and works as advertised.

Some of this customer's remote sites have very slow WAN links (some 1.5-3mb/s) servicing sometime 30-40 people. When the computer is migrated to the parent and Outlook is fired up, the OST is regenerated which clogs the pipe to the point where the business cannot operate.

Research shows this:  https://technet.microsoft.com/en-us/library/cc179067.aspx  Essentially using GPOs to throttle how much traffic will come down.

I think I know the answer to this but is there anyway way to preserve the whole OST post-move? QMMEX is not in play and I don't think a Remote User Collection would be relevant here anyway.

As always, thanks for the assistance.

Eric