You are nonplussed. You have encountered many and have collected many of those narrow type heatsinks on the right. But, all you want to do is cool down your hot house flower LEDs. It's time to FAB just the right heatsink flavour for the job. That flavour is the heatsink on the left.
Step 1: CUT AND STITCH METHOD
Your new fancy pants LEDs will enjoy the smooth flat surface of the heatsink on the left. Whoa.