Guinea pig free range time help!?

I really want a guinea pig and i know they need free range time, or floor time to get excersize. It's very important to their health and well-being, but how can i give them this if my mom doesn't want animals running around the house? And i'm pretty sure our backyard was sprayed with pesticide and insecticide. Should i sneak the guinea pigs upstairs into my piggie-proofed room? Should i convince her that she should let me give them excersize?How? PLEASE HELP!!!!