HOW TO ASSIGN/WHOLESALE WHEN HOME LISTED WITH REALTOR

I have found homes that are good potenital for assigning contracts, but the home is listed with a realtor, I know they prefer using their contracts. How do I go about this if I want to assign the contract with a buyer? Should I tell them that or get a buyer agent? I want to make sure I get the deal but not hold on to the property. Any ideas?