Using Stored Procedure result on INSERT?

I know it's possible to code a stored procedure that may be called as an expression on a SELECT statement. For example: CREATE PROCEDURE myproc(A,B) RETURNING SMALLINT... let C = A + B; return C END PROCEDURE Then you can : SELECT col1, myproc(col1, col2) ... Is it possible to do something similar on the INSERT? INSERT into mytable(col1, col2, col3) values (23, 45, myproc(23, 45)); I recognize that if one were on the proper release (7.3) a triggered Stored Procedure could be written if the desired results were as simple as col3 = col1 + col2. But my requirements are a little more dynamic that this and the function (SP) called would be determined by the calling program.