you can easily run as many instances as you want, a quick way is to just create a link for every instance that includes following parameters:
bitcoin-qt -conf=wallet1.conf -datadir=/whatever/wallet1
each instance should have set different ports in the config file (or you pass the port as startup parameter -port=xxxx, no need for config file if u dont wanna change other settings)
for more informations about config file and parameters:
https://en.bitcoin.it/wiki/Running_Bitcoinadvantage: running as many instances, even different versions of qt at same time
downside: every instance downloads an extra blockchain, no problem if you have alot of disk space