There is a thread about actual-physical devices that can interact with Beeminder via wifi and other methods [here][1].
For a timer, the physical buttons mentioned in that thread could be configured such that the first press starts a timer, the second press stops the timer and uploads the time to Beeminder.
I think you’d need something additional to be able to view the timer as it was counting up, however. Anyone have any ideas?
[1]: Getting physical aka physical buttons