Currently jcheck does not allow named branches. It throws an error when more than the default branch is found:
   "Named branches not permitted; this repository has: %s" % ", ".join(bs.keys()))

The JDK 9 Sandbox Development Forest [1], for the past year or more, has been a popular staging forest
where engineers can collaborate and do rapid iterative development. The sandbox supports many people
/ projects working in parallel by allowing multiple named branches. It would be really convenient, and a number
of requests have been received for, the ability to use jcheck on the sandbox. That is, to allow individual
branches, or the entire repository, to laxify named branch checking.

For example, one could then do:
  $ cat .jcheck/conf
  project=jdk9
  comments=lax
  tags=lax
  branches=lax

[1] http://cr.openjdk.java.net/~chegar/docs/sandbox.html