(You can also see this tutorial on my blog, Epbot, where I have a few extra process photos - and I'm actually giving away one of my two lemon grenades over there next week, so feel free to mosey on over if you'd like a chance to win.)
Ok, let's get started!
Step 1: Materials
Other than that you'll need a small screwdriver to disassemble the grenade, a thin utility or craft blade, and beading pins to hold the two pieces together. Oh, and also a Dremel to drill the holes for the pins.
If you want to paint your grenade topper as I did, you'll also need matte black spray paint and some painter's tape.