Pretty simple question...how do you do that?

The easiest way I know how is to post the GPS track on a site that supports this, and then embed it on SP. I haven't done it in a while, but the two hosting sites I've used for this in the past are wandermap.net and Everytrail.com. The good news is that, after posting the GPS track, the sites themselves will provide you with a ready made HTML fragment to embed elsewhere. All you need to do is paste it somewhere on your SummitPost page. You can tinker with the HTML if you like (I can't resist doing that), but it's not necessary.

Unfortunately, both sites I mentioned changed a few things after a while, and as a result the embedded tracks don't look as good as they originally did. Wandermap was the first to surprise me, when they stopped using Google Terrain view as background for embedded tracks. My response was to stop using wandermap. You can see the difference on the Piz Palü Traverse page: it's got an embedded trail hosted by wandermap, while further down on the page I included a static image of the map the way it looked originally.

For your neck of the woods you'll have to find a site that you like, post your track there and copy paste the fragment.

If you have a Google account, you can use their mapping tools as well, but I don't have one myself so don't really know the current status of their tools. Around the time I was first fiddling around with this stuff, I already experienced trouble embedding Google maps, let alone tracks; it wasn't as user friendly as wandermap, and when I finally got a map looking good, I found that it did not always show up properly in the three major browsers! That put me off from even trying to learn their mapping tools.