There are hotel shuttles running every 20 minutes or so to the Burlingame Doubletree, Hilton Garden Inn & Red Roof Inn. From there you can get on the Bay View Trail & run eastbound for as far as you want.
I've picked up the trail directly behind the Red Roof & ran it out to the San Mateo bridge & back for roughly a half-marathon. The trail goes the whole way around the bay so distance is really unlimited.
A couple of notes...
Behind the Virgin America HQ building you can cross a small wooden bridge & follow the road it dumps you out on to rejoin the trail in a few hundred yards or just follow the sidewalk on airport road till you get back to it.
You can stay on pavement thru Coyote Point & around the golf course or hug the bay & cut thru a small patch of woods that rejoins the trail afterwards.
There's a good waterstop w/ a restroom near the dogpark with some short/steep hills.
'Freshen Up' in the SFO International Terminal has showers for $15.