It's not unusual for an employer to make these sorts of rules. Years ago I worked in a turkey hatchery and we were required under our employee contract to keep no birds in our homes or to visit/handle birds in sanctuaries, etc. Even though we took precautions like having only certain shoes for work, shoe dips at every door and so forth this restriction was understand and accepted if you wanted to work there.
All I can suggest is that you either place the snake elsewhere since this is a short term job or consider asking them if they will supply you with feeder rodents for your snakes needs from their own breeding supply. Since you likely only need one feeder rodent per week they may will be able to accommodate you this way. I personally wouldn't get into trying chicks or messing with changing prey types since you may well get stuck with refusals and so forth that last far longer than your 6 months at this job. I wouldn't suggest you hide or lie to this employer about feeding rodents since these safeguards are there for a good reason.