Hi Chris,
Thanks for attaching your form, but I can't figure it out (I don't have access to your site so I can't preview). I don't see any filter on your repeating table either.
You can use an xpath filter to remove items that do not have a membership condition. However, as you say, this requires binding and filtering and that isn't supported in the browser.
Another option would be to add default value "rows" to your main data source and add a default value to copy the values from the secondary data source based on whether they are exceptions. This is slightly complicated as it involves setting a column in your secondary data source and having a rule on that column that triggers the comparison and copy to the main data source. You'll need to use set field actions and a counter field to keep track of where you are in the main data source.
We could show you how to do this in 15-20 minutes. Sorry, it's a bit involved for an individual forum reply.