I would disagree Blip - Saying "500ft - stabilised" would in my opinion cause an ill-advised automatic, motor response-association with the five hundred foot call.
Most standard calls become second nature and on dark late night sometimes automatic. The 500 call is mandatory and driven from single parametric cue, ones altitude and in any case is actually given to aid the detection of incapacitation of either crew member. The "Stablilised" call is clearly more conditional and in my opinion pointless.
With such a call I would fear that we train ourselves at 500AGL to say "500 - Stablised" whether we are or not. If we are talking about meeting Ops Man requirements well let me say that if by the Five hundred call you are not stablised then according to my companies OM (and I'm guessing yours) you should already be initiating a go-around and "Go-Around" then becomes the appropriate call from your PM/PNF.
Simply put the Stability Call seems redundant.