I think it could be quite easy. You just have to set the next starting point to the end of the hello. Which is in fact 5 position further. This way the text you look in shortens.

eg.

this is hello 1 and then hello 2.
The first hello is at position 9 len =5. Your next start should thus be 14. the next hello is at 26 len=5. The thing is that the user will possibly never see the text being selected as a pc handles this too fast for the eye to see.