It might be worth converting (a version of) the sproc into a multi-statement table-valued function. The performance won't change but it would give you the flexibility of "running" the code as an APPLY block within a query.
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden