T.L.Sometimes lifties get short ride breaks but I don't know of any place that does part time shifts. Most places have a minimum amount of hours that need to be worked/week in order for you to get your pass privileges. I would count on working 3-5 10hr. shifts per week.
It sounds like the job you want is in rentals. Most of the people I know up here that work rentals get mid day ride breaks between the rush of people renting and returning.
Rentals is a good one usually, i've worked in a few different rental shops. I'd say expect to work atleast 2 days where you can't ski but then after that you should either work split shifts or evening shifts as generally the evenings are busiest.
Nice thing about rentals is that in general the people are usually more driven to go ski than if you work in a restaurant or bar etc.
Alternatively you could try being a driver for a high end hotel, not sure if there are where you want to go but its pretty common for high end hotels to have drivers to take people to and from lifts, restaurants etc. again usually your workload will be first thing in the morning and between 4-9pm so you have plenty of riding time.