Can this be done in reaper?

As the title says...

I believe this is possible, Reaper has time-stretch capabilities. Check the user guide. :cool:

Probably the easiest way to do this in Reaper is to record your backing tracks (Drums, Bass etc just enough for you to do the lead) at real speed, then use the playrate to slow the song down, lay down your guitar lead, then return the song to full speed. To do this, first go to project settings and make sure there is a good algo in the "Default pitch shift mode". I use Elastic Pro but you can always try different ones if you don't like the way it sounds. Now right click on the playrate slider and make sure "Preserve pitch in audio items when changing master playrate" is checked on. Now slow it down to what ever rate you are capable of playing the solo. Record your guitar part and return the rate to 1.0. Not exactly like the video, and there may be other ways to do this as well, but give it a shot and see what you think.

In Reaper you can do exactly the same thing as show in that video. Just make sure your guitar track is using Timebase "Beats (position, lenght, rate)". The difference (not shown in the linked video) compared to Pro Tools elastic audio is that in Reaper the method will work only if tempo is constant within the whole audio item. In Pro Tools the audio item will follow also variable tempo. jnif