I'm nearby, but I'm not running Cow Harbor. I'm not anywhere near a 10k yet. I believe the Northport running club is doing training runs on the same route as the actual race, if you want to give that a try. Good luck!
~Jackie •Started c25k on 3/27/10• Graduated (finally!) c25k on 8/28/10
Chase Corporate Challenge, Central Park, NYC, 3.5-mile race, 6/16/10, in 54:41 (5k time=48:14)
Marcum Workplace Challenge, Jones Beach, NY, 3.5-mile race, 8/3/10, in 53:00 (5k time=46:34)
I live in shoreham and pretty much you will find some hills any where on the North Shore. I heard nothing matches the hills in Cow harbor though. Running along North Country Road is a pretty good climb. I was planning on running in Rocky Point and along N. Country Road when my foot heels in 2 weeks. I have been training for Cow harbor all summer long, I pray my foot will be 100% by then. If I find any challenging hills when I resume training I will let you know. Good Luck!
Where in Port Jeff are you? I live in Buffalo now, but I grew up in PJ (Belle Terre/Harbor Hills area).
If you're in that neighborhood, I'm imagining a run along Seaside Drive with a slow climb up Nonawantuc Trail, down Fairway Drive, and down Crooked Oak back to the beginning of Seaside Drive would do the trick. If you're looking for longer, less steep hills, maybe a loop starting on Cliff Road going around Beach Road, Valley Road, and up Saints Orchard Road would give you some good (and more gradual) downhill and uphill work.
Of course, if you're in the Village, you can try Thompson Street off of East Main Street (near the library). I used to bike up that as a kid. That's no joke. Likewise, anything that takes you up either East or West Broadway will give you plenty of hill work. Too bad I wasn't a runner back then.