Depends what hardware you have available to you -- if you get a thing you can set pages/banks/starting offsets for then you have a type of flash cart and it is easy enough. I guess you could do it all in software as well but it would be a nightmare hack as you have the changing of addresses issue to deal with.
If you have a flash cart for the GB/GBC you got before the everdrive took off and are looking to eek out a bit more functionality then no, give up now.