After some work with Google I find the answer to this is to intercept the paint event, draw only the background and call it done.
This correctly disposed of the buttons and the checkbox on the rows in question but the ComboBoxes are now black squares and they are actually still there--you can drop them down.
Attempting to replace the offending items with DataGridViewTextBoxCells caused a crash in the paint routine.
I need to add some total rows mixed in with the data rows. Completely non-interactive and most columns should just be blank. How do I do it??