Tools->Default values gets you more than one default row but not something that can be dynamically selected.
For that, you can create a rule and use our free qRules v1.5 tool along with an eval(eval....) expression to iteratively inject a number of rows from an XML secondary data source (2DS). Search for eval and find a bunch of posts on the technique to iterate in a funciton using it. It's a bit tricky, though and if you can't get it to work, you could always just hardcode a bunch of rules (instead of a generic one). One rule per dropdown value and one aciton per row. qRules v1.5 is your free ticket though if you want to insert rows without using code.
Good luck!