I got a "great" deal on a set of Magpul rail covers at the SAR show Saturday but cannot for the life of me figure out how to get them onto the rails! They won't slide on and they aren't flexible enough for me to set one side in place and then flex them over and around the rail. My thumbs are killing me from the effort thus far. Someone tell me what I'm doing wrong so that my self esteem can recover. Little bits of plastic are winning...