The others already confirmed that there are no tools in QMC (or otherwise) to do this. But since you asked for ideas, I thought the following might be helpful.
In the Publisher Database (QVPR) folder, open a file called DocumentTask.xml. It contains all Task definitions. Scroll down until you reach the end of the schema. Next there should be some 300 lines of single-line <DocumentTask ... /> definitions. Each line has a Description="..." attribute. Some may be filled if you tried to enter task descriptions through the QMC. Others will be empty.
You could write a PS-script or a small program to fill the Description tags. Or create an XML transformation schema to do all that using proper XML techniques.