feral cat and dogs

First of all I've pretty much read all the threads here and thanks to you all I've got a good idea of what needs to be done but I have this question. I am a dog foster. I foster labradors for the most part through rescue group but occasionally I take in terriers as well. I have 2 labs and 2 indoor cats as well as other pets. We live in a rural suburban area - basically I live in the main rural area but it has become more developed around us with housing tracts. There is still a farm down the street from us. They have barn cats which run around (and they have no interest in having them cared for I have asked). Occasionally I've found kittens and caught them and turn them in to our local no kill. The last few weeks there has been a young cat not quite adult but not quite kitten that comes around our front porch at night - I think it is all black because it looks like a shadow until it runs. The problem about feeding the poor little thing is that the dogs will find the food and run it off. It comes right up onto our porch and I would love to set up a shelter for it there but it's also the main door. Those of you who have dogs how do you entice the cat and where do you make it feel safe? Tonight I left my van in the driveway with the back open with the groceries so my kids could take the groceries in and the little cat jumped right in the car but ran away the minute we came out to get the food. My other fear is that we live on a busy main road. I only see it at night and its cold and wet out now.

It seems to want, but kind of fears, human contact. Is there any way to trap the cat and maybe vet it and find it a home?

I think if you put food out for it at a certain time every day and left it there for an hour or two then picked the food up he/she would get the idea. That way food would not be left for others to find.

Opilot mentioned a great idea for shelter in another thread. Maybe you could set up a shelter along one side of your house. She described using 4 or5 bails of straw or hay to make an igloo type shelter. It would at least get him/her out of the elements.