Another trick I found, is to use a thread like Danvilles that will lay flat rather than round in section. When wrapping over the trimmed barbs a flat thread can help cover the cut ends without too much height build up.
The other option to you is to tie the barbs on first, points out over the hook eye and fold them back over the thorax after finishing the body, bring the thread through and with a couple of tight wraps hard in front of the held back barbs they should form a suitable hackle. You can wrap back onto them to make them lay along the body better and then form your head/whip finish.
I have tried most of the above and still form some pretty rough looking heads. I do get the odd one that looks ok though.
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