I solved it like so:
#-------------
from fabric.api import *
env.user = call("whoami")
# assign CLI -H args to role 'current'
env.roledefs ={
'current': env.hosts
}
# clear env.hosts so commands default to localhost
env.hosts = ''
# function to run on remote servers
def testit():
run('hostname')
# function to run once, locally
def runlocal():
local('touch "`date`"')
def bigtest():
execute(testit, role='current')
runlocal()
--
fab -H server1,server2,server3 bigtest
...runs 'testit' on each server listed on the commandline, yet only runs
'runlocal' once, last.