Well, I think you can create a mini route for Rinnosuke (a short one). It should be a friendship route (please, don't create a Mannos... Rinnosuke love route). This will be more of a humorous route (appearance of Mannosuke) with a serious part referring to his past. The main objective in this route is to give more motivation to Rinnosuke's life and make him go out more from the shop making him meet more Touhou characters, and making him more serious about his job.
If you want a reference of a nice friendship route, play Clannad. There's a route where you can see the friendship of the main character with his friend.