This may have already been suggested, I don't have time to check so apologise if I am repeating somebody else.
Deploying to clients over WAN has always been a pain via the SEPM.
So I was thinking it might be nice if there was an installation launcher, akin to SEPPrep for example, that could be configured via an ini file and imported into the SEPM console as a Client Installation Package but, like SEPPrep, only be around 250KB instead of 400'odd MB.
My thinking is you could then copy the full package(s) to a share at the remote location once, set the path to the share at the remote location in the ini file (and installation options too) then deploy SEP at this remote location without maxing out the WAN link.
Or, as I suggested once in the past, use bandwidth throttling specified per subnet for everything and that would take care of this...but I imaging that would be more difficult to integrate into the SEPM than this installation launcher idea.