Maybe I'm totally wrong, but I'm almost sure it must be possible to force database server to RE-generate execution plans even for cached statements.
I've never used DB2 but googling a little I found: http://publib.boulder.ibm.com/infocenter/dzichelp/v2r2/index.jsp?topic=/com.ibm.db29.doc.ugref/db2z_invalidatestatementscache.htm HTH
