"I can do this manually using the built in find and new request features"
The equivalent script step is: New Record/Request
Thanks raybaudi. In this case, after much trial and error, I found that the solution was Extend Found Set. I made a loop that went through the pick list, copied the ID of each selected account into a variable and used Extend Found Set in the main layout form to add the additional records based on the content of the variable.
Either approach, a loop with New Record/Request (in find mode) or a loop with extend found set produces the same result.
Here's a link to a thread of scripted find examples--including such a looping script: Scripted Find Examples