I Select | All, then put the marker (Now) where I want the extra beats and do a Select | From = Now. Then I Process | Slide everything by the number of ticks. If you are using 480 ticks per beat and want two beats, slide 960. (I use 120 ticks so two beats would be 240.)
I had not thought about having to split clips because I usually tweak the arrangement before I have recorded audio. I am glad Craig mentioned that.