I've never used a boar brush so I don't know if that's the issue. I have made lather with a badger brush and a Captain's Choice Seaworthy bowl and Proraso Blue cream, though.
My way is to squeeze out about an almond sized amount of cream into the bowl and then fill up the bowl with enough water to cover the cream. I let that soak (and I also soak my brush in another cup) while I shower. Afterward, I dump out the water from the bowl (into a container), gently squeeze out my brush, then use the brush to whip the cream into a lather. If I need to add water to my lather, I slowly pour out whatever little water (I used to soak the cream earlier) from the container on to my brush then I continue beating my lather.
This same process also worked for the soaps and croaps I've tried it with so far.
Thank you for sharing your method! I'll give it a try.