I don't have BRMs but in the past when I needed to clear aftermarket wheels I used something like these:
http://fisherbuggies.com/bugpack/vw-bug-beetle-rail-wheel-dust-capsThe ones I have were made by bugpack, i am sure you can still get them throught EMPI.
You do have to make your own hole for the speedo cable, I punched a hole with a small philips screw driver then used a bigger one to get the hole the right size and square