I am one of those fat dudes with fat fingers so I used to have a lot of problems when I was sweeping on the lower neck. What I did was I started using my fingernails and changed the position of my hand into an 45 degree angle. at first this might feel ackward, but as soon as you get the hang of it, it is effective as hell. You could also try to press down on the fret instead of beteen the frets.