This windows application allows you to convert Photoshop brush file (ABR) or PNG picture to a VRI Verve brush file(s).  Download it here for free.
In the settings dialog you can find Material multiplayer option. Material multiplayer controls amount of the result brush material:
Verve with a custom brush example (brush 31 shown in the picture above):
Same brush in action (+ Verve built-in brushes 1-9):
Big THANK YOU goes to Taron (Verve creator) for his great help!