I have some cuttings inside, 7 pot bbg7, that started flowering like crazy, but would not set. They dropped repeatedly. I started paint brush pollinating them and still nothing. I final had another plant start opening flowers and took their pollen with a paint brush and flowers started setting.
Some plants will not produce fertile pollen or allow flower set until they are ready.
I take my phone and put it under the flowers and tap the stamen to collect pollen. Once I have a good bit of pollen I will get the tip of the brush full and lightly brush the stigma, being careful not to damage the pistil itself.
Collecting the pollen on the phone's glass makes it easy to see, being black when the screen is off.
I was able to use another plant's pollen to get flower set, which will result in a cross, but this has given me pod formation. It doesn't sound like that is an option for you, so just keep trying at different times of the day, going by your lighting schedule.
Also just thought about pollen becoming sterile if temps become to high. Not sure the exact temp, but thinking above 85°F is where it starts.
That could be the issue if you temperatures are high.
Good luck and just keep trying. Even out side, plants drop many flowers sometimes in the beginning and though out there growth.
Also see the site if you haven't already. Same concept but you won't be using multiple plants.
http://fatalii.net/Growing_chile_peppers/Breeding