Not sure if it will work by try make check RUNBTESTFLAGS="--target_board 'unix{, --param foo=blah}'"
Actuallt that runs the suites twice. Once with no extra args, once with --param foo=blah. If you only want to run it once try removing the leading comma. Thus: make check RUNBTESTFLAGS="--target_board 'unix{--param foo=blah}'" Again Im not sure if it works (I am busy building a tree ATM so cant test it for you) but it might. Kean