I've been out of Washington for the day and when I returned I found the following email from a former colleague who now does press for Sen. Lamar Alexander:
I ran across your call to arms on the anonymous hold on the senate electronic filing bill, and wanted to let you know that we really honestly have no idea who's behind it. The rules (both parties) on this kind of thing are complicated and not necessarily formal, but basically my boss just happened to be standing there when the floor staff needed an R senator to formally register an objection that was already filed. This is SOP, happens all the time, has for decades. It's why both parties always make sure to have at least one of their members on the floor whenever we're in session. The only people who actually know the holder's name are the floor staff and your old nemesis, McConnell. And, of course, Sen. Luddite him or herself, whoever it is.
Ironically, Alexander supported the bill in Rules and will happily vote for it on the floor. So you can have your members call us if you like, but we're already on your side, and couldn't tattle even if we wanted to (it would be frowned upon in the conference as a breach of senate protocol, of course). Just thought you'd want to know so you can focus your pressure more usefully.