This is very closely related to Import wallet.dat into a new Bitcoin-Qt client, but I feel this is not a duplicate because the (great) answer to that Q is for only restoring one wallet.
I used Bitcoin-QT about a year back and had two separate wallets within it. I have these backed up as two separate wallet.dat files. After some computer wipe, I now need to restore the two wallets into the one Bitcoin-QT client.
Using the prior Q, I have been able to import one of the wallets back into the Bitcoin-Qt client. I now need to bring the other one in.
How can I import a second backup into my existing account, without the need of sending my first wallets amount to a separate external wallet?