create a bunch of peace poles out of it and place them around the town and up and down the scenic highway.
http://www.peacepoles.com/

Peace Poles is officially the funnniest thing I have heard about this week.

make a beautiful bench, and put it right next to the stump, so people can go there and sit and contemplate the absurdity of there having existed this lonely tree, left in the divide of a soul-less, scalped nothing place (as all medians are), where no one can, with any safety, get out and loiter. A tree that probably only a handful of people would have ever walked next to or touched in this lifetime (touching a tree! weird!), because doing so would have put themselves at risk of becoming a blood smear on the highway, or, heaven forbid, interrupting the flow of traffic. This proper flow of traffic is of course of paramount importance in our world. We're busy people. It is so important that pretty much 100% of our relationship with this tree was as something to honk at while we drove by at 70 miles per hour.

so yes, a bench. right there, where its inevitable decay will feed the barrenness of the soil where it was destined to. a bench which will immediately be dismissed as absurd and never to be, of course, because putting a bench where humans and beast and tree are not welcome, in the center median where it would cause a traffic hazard, just could not be allowed. and who would hang out there? who would ever sit there in the median of a public highway? it's insane. 

i don't usually care for anthropomorphizing of natural objects we really don't understand deeply at all. but i wonder what it was like out there. if we would never sit in the median of a highway, and we don't really care for obstructions there, then how would it have been to be a tree there, never moving, alone, with nearly no vegetation nearby?

Have Secret Service Entertainment manage the stump.  That way we know that it will remain preserved because no events will be hosted at the stump and they will make sure nobody brings any unauthorized nalgene bottles of water near it.