Buildbot builds both 64bit and 32bit master branch (2.9) for Wheezy so just follow the Buildbot instructions, you would still use:
Code:
deb http://buildbot.linuxcnc.org/ wheezy master-rtpreempt
deb-src http://buildbot.linuxcnc.org/ wheezy master-rtpreempt
buildbot.linuxcnc.org/