I'm another success story; the Shapeways 3D printed ones worked great for me on a bike I'm building for my brother in law.

The nubs just happened to be a perfect press fit (super snug - I had to be very careful not to bend/break them as I tapped them in with a padded punch) and they aren't going to pop out unless they get a strong enough tug to break them, I think. Had the holes on my top tube been larger or smaller, it would either be too tight or too loose.

$18 shipped for three in white plastic, now I have two original black spares for my keeper bike (No, you can't have them.)