Well, if you tip because you care enough about the person on the other side, you might want to try and come up with a way to leave them a tip somehow so that there is no risk it's taken away from them, assuming that you can. Put $5 under the rug and let them know, or something.
If you can't, you can't, and I'm hardly going to criticize you for not wanting to catch an airborne infectious disease.
I was pretty miffed in the UK (years ago) when it came out that lots of companies (there it was mainly restaurants) were just keeping the tip money when people payed by card and filled-in a tip amount, so I very much made an effort to as much as possible make sure the actual people got the tip directly - even if I stood out from the crowd by doing it - as I don't see the point in tipping the company.