That's not quite burn, but close. The 317 year time-capsule has a value, and is transferrable. It destroys XMR for most functional purposes, yes, but it creates a new security, the XMR time-capsule. The effect on the float would be, probably measurably, different from the effect of a classic burn.
And it isn't so readily transferable because that would require private keys to be transferred and the buyer can't be sure of getting the only copy.
Anyway, I think you can just set the output key to be something chosen as obviously not real, like all 7s. Possibly you can set it to something that is positively invalid, too, but I'm not sure.