I have a solution (workaround).
Only thing you need to compromise on is to replace your option button with check box (but with same functionality as option button).
I hope that you have some basic skills with InfoPath rules since my solution is all rules and it is not so simple (but you asked for no code).
Add two new columns to source list:
IsChecked – Type: Boolean Default value: False
DummyTitle – Type: Single line of text
My source list:
Refresh data connection to source list in InfoPath, delete option button and just leave Title (as label/calculated value or textbox) – this is setup you already have.
Or recreate your repeating table from scratch.
Add newly created fields to repeating table. IsChecked as CheckBox, DummyTitle as TextBox.
Add one more field to your main InfoPath data – SelectedItem (to store current selection) and add it outside of repeating table as TextBox.
InfoPath design view:
Add two rules to IsChecked CheckBox:
Condition: IsChecked = TRUE and DummyTitle != (not equal) Title
Action: Set a field's value: SelectedItem = Title
Condition: IsChecked = FALSE and DummyTitle = Title
Action: Set a field's value IsChecked = true
Note: Rule B is ensuring that check boxes in repeating table are working as option buttons. Only one can be true.
Add rule to DummyTitle textbox
Condition: DummyTitle != (not equal) Title and IsChecked = TRUE
Action: Set a Field's value: IsChecked = false
Add rule to SelectedItem textbox.
Action: Set filed's value DummyTitle = SelectedItem
If you followed my steps and if I didn't make any error in explanation you will now have working example of my solution.
Note: For production solution you can hide DummyTitle.
I used MOSS 2010 platform and InfoPath 2010 (but since there is nothing so special in solution it can run on 2007). I can even send you my xsn file for reference.
I have tried to write things down as simple as possible so no additional explanation is included. Like always: I will provide more info if needed.
I haven't touched InfoPath for year so I will not exclude that there is some simpler solution.