A new or fairly new concrete patch product which has latex mixed into the product allows for movement and a very good patch job. I have used it in smaller areas just like your describing and it is staying put.
YOu don't have to use rebar or other things as you know concrete will not stick to concrete and stay.
Check this out, they sell it in all home centers.
You could build a new form or frame, rent a compressor and blow off all the debris and dust, chip up the foundation alittle to create areas for holding, then pour. Make your expansion joints also.