How would you run a defend-the-building type oneshot?

[Wednesday Boy]

I thought about just handing them the XP, but these guys have been counting down to 1000 for two sessions now and giving them free XP off-session may feel like a hollow experience.

I'd check with them to find out if it would feel like a hollow experience to them or not. Personally I'm always glad when the GM gives us a little bonus XP when we're within a nose, so we don't have to wait an entire session before leveling.