i wondered about that as well, same processor and cooler. i just used my trusty ole' plastic grocery bag stretched over a finger method to apply a thin layer to the heatsink base and the cpu heatspreader. it seems to be working just fine. I didn't worry about trying to fill in all the gaps or anything, didn't really make much sense at the time, plus arctic silver 5 is kinda expensive to be wasting.
I was reading a review of the Xigmatek s-1283 (can't remember where) and the guy tried different methods. The best method he found was to apply a thin line directly along each heatpipe and then attach the heatsink. This ensured there was enough TIM between each heatpipe and the heat spreader. This method uses more TIM than usual, but the excess will find it's way into the gaps rather than squishing over the side.
The reviewer found the traditional method (line of TIM down the center of the heatspreader) did not allow the TIM to spread out to the outer heatpipes.
It's important to note that it's only important the the heatpipes have good contact on these types of heatsinks. The metal blocks between the pipes are there for stability; they transfer little or no heat.
Also, read this:
When applying thermal interface material to the Xigmatek HDT-S1283 exposed copper heatpipe 120mm CPU cooler, it's very important to understand that most TIM's used with aluminum coolers will cause oxidation to the copper heatpipes upon contact.