Now that it has been 6.8 years since the last post, I feel the time is right to add to this thread.
Writing an LOR is a pain in the butt.
IMHO, most people who are asked to write an LOR are agreeable to the idea of YOU writing your own letter in DRAFT form for them to review.
You should know best about the job that you are targeting and you should be able to "nail it".
The idea of a sealed envelope and not seeing it something I've seen in academics--not in aviation.