Populate field 2 with a query based on field 1

I'm hoping GF 1.6.3x can do this:
1) Populate dropdown with values from a custom taxonomy (I know GF can do this)
2) Once selected, populate a second dropdown with Posts in that taxonomy.

I have step 1 done, but need to query based on step 1 value, and then populate step 2.

Some ideas:
1) Populate using jQuery?
2) Can we populate using the Page Break feature? Pass the param from step 1, to a query run in step 2?

Thanks