Yes Mike, I have and it worked well. This summer I fished 3 days (nights) on the Ribble and fished 10 mm boilies over a bed of stewed wheat @ pearl barley and pellets. Both of us had a dozen barbel to 8lbs 6 on this as well as several chub each.
I have also used this combo for river carp and bream . You can have confidence in it. I actually flavoured the mix with curry powder and added garlic puree to it for some real honk. I'd be interested in your (and anyone else's) results.
I've done something very similar to Keith with good results. I mixed together wheat, groats and buckwheat and flavoured it with curry powder. It worked best where hemp had been used a hell of a lot and I suspected they'd got wary of it.