Holding concrete OUT of block holes,,,product???

Old house, enclosed porch, corner settled away MANY years ago,corner was raised 20 years ago and is now stable. previous owner had a big hole out back which collected rain water from a roof vally,,,fixed 20 years ago also.

Now I want to 'mortar' 8' of crack where it settled,2" on worst to zero at best. But it is over the top of hollow old block. I really dont want to core the block,,or leave it run down inside block holes.

Question is will low expanding 'great stuff' made for windows and door work to hold this mortar out of the holes?? Or would the more expanding type be better? I was told the expanding type would crack the blocks,which I dont want to happen. I also considered using newspapers to stuff the holes first but not sure that would hold it either. Cant clean inside those 90 year old holes so no way to get good adhesion with 'anything',,, thoughts???