Just tried with MIDI items, not audio, but ripple works fine during paste, pushes the right side away by the width of the copied material. Using Tiger on G5. Reaper 3.11.
This is not yet part of Reapers feature set. You could split and before pasting. That's works nicely. Should you seriously require this, prepare and post a feature request in the . I've just posted one such request for an improvement of the editing feature set. If you require any help putting a feature request together, just pm me. I've gotten pretty good at such things :) . Btw, I edit and mix dialogue for tv/film.