Hm.. I'm assuming Ren heals you when you are poked, and that when he heals you your HP is above 3000. If so the following *should* work.. but I'm kinda new at this script stuff.
#IF (lastHP<%1) {renpoked=FALSE}
#IF ((@renpoked=FALSE) AND (%1 != %2) AND (%1 < 3000)) {poke ren;renpoked=true;lastHP=%1}
The first line checks to see if you gained any HP since the last prompt (presumably from being healed by ren). This might not work if your mud regenerates you in combat though, but gives you an idea.
You're gonna need to create a var named renpoked and lastHP, natch!