You can't do this in blitz natively as you don't have control over the patterns. You'd need to write your own tracker to do this. I did start writing one a while back but didn't see it through, but the idea behind it was so exactly this sort of thing could be achieved.
You'd need to use a DLL as you mentioned to control this, no idea which one, but you might want to look at the bass.dll however that has a fee attached.
You'd need to use a DLL as you mentioned to control this, no idea which one, but you might want to look at the bass.dll however that has a fee attached.