Why can't we buy RP on the Post Game Results Screen?

Let me just say there are very rare times when I want to gift a random person a skin. After my first good game today, I wanted to give my Janna support something nice for helping me carry a game. I couldn't do this, however, because I had no RP at the end of the match to use on her. I'd like to be able to buy RP in the post game lobby, or just buy the gift without going through the RP purchasing process. Is that possible to implement?