You might have an (html) id on each "row" from the database, and some way for the user to select a row to edit (e.g. onclick), a javascript pulls the cells from the table and puts them into the form elements that also have id's. With css visibility you can even hide the form until it's needed.
hth
Edit: I forgot to address your question about telling formbuilder about this, -you don't need to do that, just provide the hooks (id's)