If they're letting them out when they shouldnt be, kidnap them and drop them at a local CP or RSPCA saying you found them abandoned in a box. I honestly would have no shame in doing this - its for the cats benefit, and i wouldnt give two hoots if the people wondered where their cats had gone.

I actually acquired my cat in this way....horrible area, lots of crime and violence, very young unneutered female crying for food so we fed her and she slept outside all night and day for about 3 days. First day we found her we went around to the address on her shabby, too tight collar, and told the (obviously drug addicted, with 2 screaming toddlers) woman we had her if she wanted to come and get her. The houses yards literally back onto each other. Her response was "she'll come when shes hungry." She didnt even bother to come and shout. I even offered advice re: neutering, jabs, etc and told her she could get a free neuter voucher from the CP. No response or care.

3 weeks later (and a carefully planned kidnap operation where millie-cat went to my mums house for a 'holiday' whilst moving plans were finalised), she moved in with us in a much nicer area. Shes a year old now - the most affectionate little thing ever, very demanding and vocal, but still suffers with flea allergy and is a COMPLETE scrounger - she doesnt seem to realise that these regular meals wont just disappear!