[Help-gnu-radius] Extending Radius

[List User]

Objective:
to change a Session-Timeout value in Attribute table, *BEFORE* radius runs
query to get this timeout for a specific user.
in other words, session timeout is dynamically calculated for each user upon
connection.

How should I approach such problem (mySQL does not support Stored Procedure,
so I can't aggregate two SQL statements):
I can only come with the solution of  adding C code to radius to execute
custom query

thanks