You should be able to get an employee pass, it's what I did at all the airports I commuted into/out of (IND/LAX/OAK). Contact the parking authority and see what a monthly pass costs. Depending on how long you are gone, it may make sense to pay daily rather than a monthly/quarterly pass.

Also, at my airline, since employee passes are free at ORD, we are not reimbursed for parking (it is capped to the maximum parking rate at your domicile, if that makes sense.)