Hey Phillip,
We took a bit of time to get to the bottom of this one, but yes I can confirm this can be done in method. To do it just like QuickBooks, it is a very advanced screen, and we are working on getting it created for our users as soon as we can. Once we have that, we can send you a copy of it to work from. We hope to have something very shortly.
We created a functional test one yesterday ourselves. It was very simple but it worked fine.
1. We created a screen based off of the BillPaymentCheck table.
2. We put a detached grid on the screen, based on the Bills table.
3. We dragged the required fields onto the screen, and put a button on there.
4. The button first saves the screen. Then gets the active recordID from Value From Session into an action result. Then it loops through the grid for checked rows and for each row, inserts a record into the billpaymentcheckapppliedtotxn table. Finally, it then saves the screen again to commit the BillPaymentCheck to QuickBooks.
The amount being paid is equal to the balance of the bill. This is displayed in that grayed out amount box. It works as a sample situation, just a little clunky. It only works if you have only checked one Bill in the grid and that Bill matches the Vendor selected in the screen for the BillPayment.
If you are stuck, doing what I mentioned above, if you active the MethodSupport I can log in and import the quick screen that we made to test this out.