If someone does decide to match you, they should also announce and retroactively ask someone to match them, and so on...
The 'forward' way to do this, "I will donate $150 if someone else commits to this statement.", may or may not be better.
And if they take long enough, I'll match that person myself. :)
I just donated $150 to the Singularity Institute. Would anyone be willing to match my donation (as in, donate at least $150 and tell me you did so)? A first-time donor would be ideal, but anyone would make me happy.