define persistency with irule on gtm

i have few web servers that are behind gtm. the wide ip is using topology as the service is global and the pool level is using global availabilty. the service requires stickness persistency so hence why we using global availabilty but the problem is the server in the pool with the lowest order is getting hammered. I was looking at irule to define something on the gtm to utilize the rest of the server within the pool like a rounb robin fashion and still maintain persistency. global availabilty doesnt really achieve that as it always return the same server in the pool with lowest order. Is there anything available on the gtm to achieve what i want? i want to be able to utilize all servers and keep my persistent.