Sorry a little late in replying to this as I've been on hols and unable to sign in to post..
What I did was had a look at the PIR and altered it so I got dry contacts - If you post a photo of the PIR PCB each side it may be possible that you can remove links to make it work.
Also its worth pointing out that a lot of 240v PIR's are actually 24v so can be converted back to 24v - You can also buy them from ebay that are exactly that if you search for 12v external PIR (obv they are 12v - think 24v is less common to buy but some i've had are certainly 24v - have a look at the relay coil voltage to confirm.
Also GJD do a nice range of external PIR's but they aren't cheap but can be dual tech.
David