1. How often do you travel between Europe and America? (I mean, swapping SD cards once in a while is no big deal...)
2. Not sure if the following will work, but it's worth trying: US map is much smaller than Europe. Suppose you try to copy the US files into the device's internal memory into the correct folders and sub-folders(!), after having erased the old Europe map) and see if the US map is still acceptable.
If this works, you'll have again two maps simultaneously
Bookmarks