Nigel,
There's a great feature in Reaper called 'Stretch Markers'. With these, you'll easily be able to add your own pushes (or pulls) to a Realtrack. Once you get the hang of it, it's pretty quick to do.
If you go to Youtube and then search for Reaper Stretch Markers, you'll be taken a few videos that will show how to do it.
Regards
Noel