Prepare your bbq for indirect grilling. (If indirect isn't possible, you can use direct but it will take less time and you will need to watch more closely to make sure it doesn't burn.)
On a cutting board, chop the garlic and thyme leaves very finely. Sprinkle with the sugar, salt and pepper. Use the side of your knife to mash it all together until it looks juicy. Transfer the mixture to a small bowl and stir in the olive oil.
Lay the prosciutto slices on the cutting board. Spoon 1/4 of the garlicky thyme onto each slice. Using a toothpick, secure one end of a piece of prosciutto to one end of a cob of corn. Wind the prosciutto so it covers 1/2 of the cob. Stab in another toothpick. Use another slice of prosciutto to cover the other half of the cob, stabbing as necessary. Repeat with the remaining cob and 2 slices of prosciutto.
Transfer the cobs to the grill and cook over indirect heat turning occasionally for 15-20 minutes until the prosciutto is very crispy. Remove from the heat. To eat: Messily crunch and crumble your way through the prosciutto to get at the garlicky kernels beneath.