Some time ago on Ravelry someone made a remark that asserted you can't blend fibre on a blending board. Her reasoning was that for carding to happen the fibre had to be transferred repeatedly, and it had to be transferred with another toothed tool. Just because she could not see past the most common use of a blending board (rolags), does not mean it can not be done.
Neither hand cards not drum carders mix fibre thoroughly with only one pass. No one will stop you from putting the fibre on the blending board as many times as you like to blend it as much as you like. I get so pissed off when ignorance presented as knowledge hinders other people's creativity.
Yes, you can blend fibre on a blending board. This is how I did it.
I have this hand painted top which I wanted to make more uniform colour. I laid it all out and tore it into pieces horizontally. (This brush didn't work because the bristles were not stiff enough. I ended up using a cat brush, but a hair brush with natural bristles is on my shopping list for the next time.)
I loaded each piece onto the blending board, brushing the wool down occasionally, until I had a nice size batt. Turns out the size blending board I have makes six batts out of 100 g of top. Next time I want to blend a top I'll tear it into pieces divisible by six, then put them in six piles and distribute the colours evenly across the piles. This pre-mixing could save me a pass.
This time I did three passes. For the second and third pass I took the batts, tore them into three strips, tore those in half, and made six new piles of mixed pieces. This is the result of the third time I loaded the blending board and took off the batts.
Then I tore the batts into half vertically, and attenuated those strips into roving. And that's it. Not at all complicated, and entirely possible.