I've helped with a similar type race in the past where if everyone finished at their handicap, everyone would finish together. Is that what you are seeking to do?
You can create a wave offset table. It is described in the help files. Basically you will have a bib number and a wave offset time in a csv file.
The biggest problem you may have is making sure everyone starts at their correct time. How I would do it is assign the wave starts as you are asking about. In some manner create a list showing either a time of day for each person's start or a sheet showing time from the first start but... unless you have a good starter that keeps them to that time you may want to put a start mat there as well so their true time is recorded not just the time from when they were supposed to start.
If it is just a "predicted time" event, RD has that function as well.