Just use armory, it has multiple wallet support. Otherwise every time you switch to another wallet.dat you have to shutdown bitcoin-qt then run -rescan for that wallet.
Please don't supply misinformation.
You can use file->open wallet to load other wallets. You will have to use the command line once to create the wallet though. electrum(or .exe if you are on windows) -w /path/to/wallet/for/instance/saving-wallet.dat.
The next time you want to switch you can use the open wallet feature.