Connecting a switch to a jack
All you should need to do is use any jack with 2 connections that will fit where you need it. This can be a phone jack, RCA or even a 2.1x5.5mm power jack. Just take care to ensure that the jack you use is not easily confused with something else - like using an audio jack where you can accidentally plug in headphones, or a power jack you can mistakenly plug a wall wart into.

I will use a mono audio jack as an example, but you can use whatever you find that works best. Here is a schematic:



Procedure


Learn to solder if you haven't already.
Determine if you need a latching or momentary solution. If you touch the two "dots" together for a short period, and the computer stays on, you just need a momentary switch. If you have to keep the two connected for the computer to remain on, then you need a latching switch.
Wire your two "dots" to the two connections on the jack.
Then, wire a mating plug to a SPST (single pole single throw) switch. This can be a rocker, slide, toggle, or pushbutton - whatever you prefer - as long as it meets the requirement determined in step 2. Wire the plug so the tip goes to one switch terminal, and the sleeve goes to the other.