I find that mixing frozen in with live food helps to get picky fish to eat frozen...but adding pellets to frozen/live food rarely works since the fish can easily tell the difference and will ignore pellets.
How many fish are you trying to feed, and how fat/healthy are they? You may have better luck if you skip a day of feeding to get them hungry, then introduce just pellets into the tank for a couple days. If they're hungry enough, they should start to go after the pellets.