Having looked at LASORS, I reckon foreign flight time is acceptable towards a PPL even with the minimum of 45 hours. It states that all training shall be conducted on a/c with a C of A issued or accepted by a JAA member state. Fair enough, let's assume that an Australian or FAA registered plane is not accepted for some reason ..
LASORS states that the minimum requirements for a JAR PPL is 45 hours of flight time which must include the following training requirements: 25 hours dual and 10 hours supervised solo (inc cross country). That leaves 10 hours of flight that is required for the PPL issue but that is not required as "training" therefore looks like it can be carried out on a non JAA approved C of A a/c.
Make sure you have the CFI sign your logbook that the hours are true and I reckon you'd be OK with 10 hours of "foreign" flights even in the minimum requirement of 45 hours for a JAR PPL. Given that most people take more hours to complete, any hours are "good" hours early in your training and I reckon that a PPL with say 50 hours, 15 of which were acquired & verified overseas would still be acceptable.
Why not email the CAA with the specific question? I found them helpful and respond within a couple of days. My money's on it still being OK to pick up some experience on your holiday but I agree going solo abroad is a completely different matter requiring pre approval, medicals, provisional licences, air law etc.
PS Not sure where in Oz you're going but if it's Sydney, then Bankstown is the big GA field there.