Basically, if you're employed in the UK, get paid there, pay rent & utilities there for 6 months then you're fine. But you DO need to have all this as C&E absolutely HATE letting you away with it (as they see it). If you still own a house there, then you can say you're a tourist and be safe for a good few weeks (months?). If it's taxed and insured in the UK, and you have all the proof of that, then what's to stop you moving over here every second week ? How are they to know ? The onus is on them to prove liability, at the end of the day.
If you do all the above (get paid there, pay rent there etc) but still live here for part of the time, then you can still be done. I know of people who are from Derry but stayed with their partner in Donegal a few nights a week and the C&E stopped them one morning saying that they've been noted staying in the South for so many nights over the past month or whatever and threatening them with seizure of the car.
That could all be a spiel to have the word spread that they're out and about and watching, admittedly...but it worked.
Also, and this could well be an urban myth, but they can only apparently seize the car from the owner. So if it's registered in another persons name, you're safe (temporarily).
I reckon the first scenario should cover you however.