Data point: twice in the last week I've loaded multiple VGCs to Serve at RA, once 2x$500 and the next time 4x$500. I found it helps to just be honest - tell the cashier that you want to load $x, but that you think Serve has a $500/load limit, so you'll need to do a few consecutive loads. This at least worked for me the two times I've tried so far. (The first cashier knew about the $500 limit and was happy to do multiple loads, and the second one was clearly less sure about how all this worked, but confidence and friendliness walked them through it.) Then you don't need to even mention that you're using multiple debit cards. I probably will stick to 2x$500 from now on, though, just so as not to raise suspicions.