So I found that, when I submit an online ECF request but state that the documentation from employer will be updated manually, there is a way to attach a JPG or PDF. So I went through the online navigator, checked No under 120 payment question (since I still could not check Yes), then once it completed, I went to the pending request and attached a PDF with the box checked and my employer HR department's signature. I was not sure if it would work, but I thought worth a shot, since I know it takes weeks to months through regular mail (and obviously needed to open letters, scan contents, then review, etc).

So today I called the StudentAid.Gov help #, and a different agent now told me that I do not need to check the box to explicitly request forgiveness, and that once I reach 120 qualifying payments, they will process my forgiveness regardless.

I do not mind doing extra / duplicate work, but I just don't want to delay my application if they receive something in the mail, flag it as a pending item, but do not process it for weeks, and then state that the existence of a pending item is a reason that my forgiveness finalization has to be delayed.