Selecting persist profile

I'm sure I'm missing something obvious here but I can't figure it out.

I need to achive something like this in an iRule:

 if { statement } {
   persist profile_one
   use pool pool_a
 }
 elseif { statement } {
   persist profile_two
   use pool pool_a
 }
 elseif { statement } {
   persist none
   use pool pool_a
 }

Where profile_one and profile_two are two different cookie insertion profiles (different timeouts)

What I need is how to make the persistance profile selection above work, "persist profile_name" is clearly not the right syntax.

It seems to be possible to do "persist cookie insert"

but that appears to use the persistance profile associated with the VS which isn't really what I need.

Any ideas, scratching my head here.