There may not be much that you could do in a situation like this. Try to find out why this is the case, as:
- Some letter writers may effectively curtail the multiple back and forth of having to constantly update and edit LORs by refusing to share it with anyone but ERAS;
- Some letter writers truly believe in the value of a waived LOR, and take extreme pride in the traditional approach to recommending candidates, hence they will not write an LOR if the candidate refuses to waive his/her right. In this case, ask the write if there will be anything in this waived LOR that could cause a reader to be concerned, and if so, its probably best to not submit that LOR to any residency program.
Click here to read the pros, and cons of doing so.