I have purchased a Gigabyte 970A-UD3P AMD mobo and have been sending a lot of confused ppl on here regarding temps o on these series of boards and other odd issues which very few ppl can help solve. Most do not even know what they are talking about in some cases, but I digress.
With your question, I'd say your best bet for a cheap and easy way to get your fan to stay on the NB heatsink, is get 2x sided tape and stick it on the heatsink so your fan can push or pull air from it. Most ppl never consider cooling these items, like VRM and NB, but then give bad reviews of products that they themselves overheated. Anyway, I ALWAYS over sufficiently cool these key parts. Esp if you like to oc, you will NEED good cooling.
I personally used a cpu fan from an FX6300 for my NB, by putting zip ties thru the holes to form circles which I used as "feet" So my fan wouldn't sit directly on my video card. The ties formed a loop about the size of a dime. Then, I used wires for training tomato plants and used the top two screw holes to suspend the fan a bit. It now sits beside the NB heatsink and blows the air thru the fins and out the back of my case where a120mm fan sucks out that heated air. For my vrm, I used a Noctua 92mm and utilized an L bracket from Lowe's. I screwed it in and set the fan to blow upward but directly on my VRM heatsink. After these cheap mods, my temps dropped dramatically. Over 10 deg C from just doing the method you'd like to do... to tape a fan right on the heatsink. The thing is, the fins need a lil room to get air moving. So you are better off ting to think up a setup where u can suspend the fan to blow on the NB w/o touching.
I'm a nut when it comes cooling on pc builds. But it extends the life of your hardware, sio idc if I'm nuts. Another thing is, I open HWmonitor as soon as I start up Bc I always monitor temps. Speaking of HWM, I originally signed up for this site to post about ppl disputing what the Gigabyte mobos temp sensors measure. I know for a fact, one is the socket temp, one is the VRM temp and the other is the Northbridge sensor. They are all accurate on my board. But Temp 0 I believe is the socket temp, temp 1is NB, and Temp 2 is VRM. I may have the orders mixed a lil, mainly 0 and 2, but I know that's what they correspond to bc I said, I've cooled each part and seen temps drop one by one. Many ppl on the board here say the VRM or socket temp is just an ambient temp sensor. U can quickly disruptive this by taking the side off your case. Run a game under load, or prime 95 it, put a house fan directly twd your open case, n if the temps drop dramatically (like 15+ deg C), then yeah... it'd be ambient. But the latter is not what happens. My ambient temps are much lower than what the sensors read. I've checked w a good quality ir thermometer.
Anyway, if you need more personal help engineering or designing custom brackets for cooling, email me and I can help whoever needs it.