Agreed. I also run long hives, 4 feet long. If the hive is not packed full, set an entrance feeder inside past the frames. Or set a baggie on the bottom in the same place.
Our hives are also designed so we can use top feeders, and with an adjustment that might work for you if your long is completely full of frames. If you've got a shallow super or a large shim, put it on top of the hive at one end so it butts right up against the other inner covers, put a syrup baggie inside on top of the frames, then use ply in place of your outer cover to temporarily close off any unwanted extra entrances. (This is why we use 3 migratory covers, so we can set a super or top feeder on any third of the hive without creating new entrances.)