set Persist iRule to match across virtual server

You simply need to configure a persist profile of type source address and check the "across virtuals" box. Then add this profile to the virtual server. It will act as the default. Then, when you don't want to persist based on source address, you'll need to invert your logic in your rule and execute a "persist none" statement. For example:

 
 if { not ( [IP::client_addr] starts_with "195.53.125.1" ) } { 
    persist none 
 }