Replacing baseboard heating

I want to replace a section of the baseboard heater without having to remove the pipes. The existing unit has metal hangers that can be removed and then the piece that screws into the drywall can be taken out. The problem is that the replacement unit (Slant/Fin) has hangers that slide on from either ends. Ive been unable to figure out how to install the hangers on the wall piece and then slide the unit behind the pipes. There does not appear to be a way to install the back piece first and then slide the hanges for two reasons. First, there is no clearance between the ends and the walls. Second, the hangers, no matter how they are turned and twisted, will not fit behind the pipes even when off of the back piece. I checked at a local home improvement place and the salesperson said that the product is for both new and replacement installation. Any suggestions? Thanks, Dan.