I tried to order a new Mini for that same reason.
When I called about a CTO I wanted to do, the person at MacMall said they would have to special order the device and (listen to this) regarding my wanting 8GB of RAM, they would have their warehouse install that upgrade.
I hung up and decided to order my Mini direct from Apple the heck with the taxes since I wanted original RAM not some bs like that. Soooo be careful what you do to save a few bucks.
Remember if you ever need it serviced at Apple and some odd RAM has been used you have no "original" Apple RAM to put in before going to Apple.