I've never succeeded at feeding pollen anytime except early spring.
What I feed, when I do, is real pollen if I can get it. It's pretty expensive so I sometimes mix it 50/50 with pollen substitute and then make a paste with honey until it's like bread dough. I buy both the pollen and the substitute from Brushy Mt. I may try the BeePro from Mann Lake one of these days. Everyone who uses is swears by it.
There's plenty of pollen already out there for forage but you have to get the bees to want to store it and I don't know any way to do that. Maybe if you take their frames of stored pollen they would store more.