Use views to produce list of terms with descriptions
A easy workaround could be to attach a regular text-field to the terms, instead of using the hardcoded description.

Update: After taking a quick peek in the code, it does look like filtering on descriptions are not supported. This could just be a simple oversight.
There's an issue here, which claims this functionality has been added. I can't seem to find it, so I attached a new patch and reopened the issue.

Update 2: Dereine has commited my patch to D7. You should now be able to filter on term descriptions with the dev version.