Hello Phil
I don't know if it would work on Mainline , but on a Hook Length Braid sometimes when you cast the strands in the braid separate and air gets in ; what you can then do is make sure the Braid is wet and run it through your fingers to squeeze any air / bubbles out .
What if you did a big chuck with just a Lead , and then slowly retrieved with the Braid pinched through a damp rag ? .
Failing that ask Carpmachine , doesn't he use Braid as Mainline ? 😁.