No, there is no way to do this via the Q2A interface.
However it is possible by editing the database. Find the ID of the answer - it should be in the link of the "answered" text, something like ?show=a#### where #### is the ID.
Then find the question you want to make related in the database, and put that answer ID as the value for the "parentid" column.
You could also make a plugin to add that functionality.
