User-defined aggregate functions and OLAP windowing

Friends:

In v8 or v9 LUW, if I were to write (in Java or C) my own user-defined
aggregate function, would I be able to use it in an OLAP windowing
clause as I could use, e.g., COUNT or SUM?

Example:

SELECT
   JEFFS_UDAF()  OVER(PARTITION BY SOME_COL)
FROM
   SOME_TABLE;

--Jeff