It doesn't have to be called "wallet.dat", right? That would be too obvious. Can you call it anything, with any extension?
Bitcoin-Qt is just not so trivial to me to use since the trivial way would be to have an option File -> Open wallet (at starting the program), then enter password if encrypted. TrueCrypt for example is trivial in this way, you select any volume, type in a password, mount, and dismount images.
I don't understand that either that you encrypt your wallet.dat file, close the client, open the client and it doesn't ask for your password?