Hummm, here is an idea...
Some one should build a similar product that is an add-on fan to exactly fit the back of the docking station. I'd buy one!
So, is it really interesting to buy this colling pad ? If you tell me that the results are very good I will buy one for my SP3 i7 that I'll buy in a few weeks. But I'm little bit affraid about those kind of articles: http://www.ubergizmo.com/2014/08/microsoft-surface-pro-3-with-core-i7-faces-overheating-issue/
Honestly, you shouldn't be afraid; that's one person's perspective, and that person almost certainly doesn't even own an SP3!
Friend you should just take it instead from all the members here on this forum, and read what they have to say. The vast majority of them are happy!