I imagine it would be relatively difficult to fit into the XP nodelet code, where it doesn't really belong. A simple solution that addresses the elusiveness of the XP nodelet messages that should also be much easier to add somewhere: when you reach 490 XP, you get a root /msg saying something along the lines of the text that was proposed. That will probably also attract more attention, ie not be so prone to conditioned click-through-EULA reactions.

Makeshifts last the longest.