They charge £5 for entry on the Open Gardens Scheme - I’m sure they’d let you walk thru for a fee. And it does go to charity. Still, if you’re on the Forest track, you could cut down the fire break and then follow the forest edge to the road to avoid their garden. Although it’s not always possible/easy to walk fire breaks.

The road in question is very rural, you could also go past Errogie and then follow the east side of the Loch Mhor to Aberchalder.