There really is no other way to preserve your E-500s but to use them on someone on your flights. If you don't have anyone traveling with you and your E-500s are going to expire, you could do one of two things:

1. Go to Coupon Connection and say which flights you are going to be on in the near future and if, by chance, someone else will be on those very flights (or at least one segment). You could then upgrade that person for the same segment(s) you are on.

2. When you go to the gate, look around and see if there is a likely candidate who is traveling alone--someone in uniform, an elderly person, etc.--and see if you can upgrade him/her as a gesture of generosity and goodwill.

Otherwise, I'm afraid it will just disappear since you didn't sign up to have E-500s convert to RDMs.