Hi Paul,
You need to do the following:
1. Add dummy open end box in last row using jquery
2. Hide corresponding checkboxes
3. Add open end grid with one row and hide its boxes
4. Now connect dummy open end boxes with open end grid such that whatever is written in those dummy boxes gets copied in this OE grid
You would need to get your hand dirty with some jquery skills for this, in case you need any further help, inbox me!
Regards,
Saurabh