how to destroy excess iodomethane in reaction mixture?
Yes, you can destroy small amounts of methyl iodide by hydrolysis with an aqueous solution of sodium hydroxide. You can just add some sodium hydroxide solution to your reaction mixture, if your molecule is stable to basic conditions.

The reaction is: $\ce{NaOH + MeI -&gt; MeOH + NaI}$

From: "A Comprehensive Guide to the Hazardous Properties of Chemical Substances" by Pradyot Patnaik, 2007