In the past I did a Free Form SQL (FFSQL) report in MicroStrategy on top of a PL/SQL function which returned a 'table' (Of course that was an Oracle database, more info about returning a table with a function here).
So what you are looking for is something doable.
- You can use the prompts in FFSQL report as parameters for your function
- Then you have to map the columns of the returned table as attributes and metrics returned by the FFSQL report
This is something I did in a very old MicroStrategy implementation to provide writeback functionality: the users were allowed to update some values in some tables and the function returned a Success or Error message.
As you can imagine this was not a standard Data Warehouse solution, it was more an hoc solution for an operational database.
My suggestion is to avoid similar solution if not necessary and prepare in advance the tables/rows that you need. Of course in your case you have already the procedure ready so you have just to figure out how to combine it with MicroStrategy.
Some useful readings:
TN37783: Instructions to use stored procedures within Freeform SQL reports in MicroStrategy 9.x against different databases
Using Prompts in Freeform SQL Reports