These holes just weren't worth mending, they were to big and the yarn was of a really bad quality (don't buy yarn without information about what kind of fibres it is made of).
But since I have been told not to waste yarn I did as my mother often did.
I cut off the part with the useless yarn and frogged the remaining material back until I reached the point where I wanted to start the new foot.
I picked up stitches and used a yarn of better quality for the foot.
I also checked with myproject book regarding needle size, amount of stitches and other particulars regarding the sock.
After some knitting I had a pair of socks almost as good as new.