How to redirect if less than x nodes are avail

I would like to do something similar -

I need to configure a pool/vip so that if < X nodes are available - the entire vip is unavailable. Nightly this applcation is restarted, the first node that comes online gets hammered by connecting clients. The way our application works, combined with persistence method we use, means that nearly all clients will be on one node while the others are empty.

Would be awesome if I could just to use something simple like:

pool my_pool {
lb method member least conn
min active members 2
monitor all some-test
member 10.12.10.7:80 priority 1
member 10.12.10.8:80 priority 1
member 10.12.10.8:80 priority 1
}

but doesnt look like that is how priority group act works.

Slow ramp time doesn't work since for some finite amount of time there is only one node available in the pool.

Perhaps an iRule would be best - anyone have anything they use or ideas?