You can do this in the existing preSubmit() function in mayabatch.py:
def preSubmit(cmd, job):
# Handle renderer-specific callbacks
if cmd.package['-renderer'] == 'mi':
return preSubmit_mi(cmd, job)
elif cmd.package['-renderer'] == 'turtlebake':
return preSubmit_turtlebake(cmd, job)
job['env'] = {
'foo': 'bar',
'foobar': 'bat'
}