Yes, quite easily.
All of our remote users where I work have 2 ADSL connections, a business line with Telecom which we set up for them and their own home connection with whoever they want. This is not a problem and quite easily set up.
You have 2 pair in most phone cabling, so if your house wasn't made in the early 1900's you should be fine and there won't be much of an install cost.
But yes, as others have said it would be a lot cheaper to just pay the difference for unlimited. Tell them you'll clean the bathroom as well :-D