I’m looking to solve a similar scenario. If you use an android phone already then you are completely in luck. I use an iPhone so will have to source an android phone to make this work. I’m in the process of obtaining a Sony Smart Watch 3 which I will pair to an android phone running xDrip+. Heading out for a surf I’ll make the smart watch become my primary ‘collector’ as it is referred as. BOOM hopefully that should result in the dexcom G5 working stand alone with a smart watch.
there is a good blog called travelbetic that talks about his solution. I have been trying to solve it without taking my phone into the water as would currently be required per his methods.
http://travelbetic.com/2016/09/14/continous-glucose-monitor-cgm-data-on-smart-watch-while-surfing/
https://www.youtube.com/watch?v=Awvbueg8sIg this video shows you how to run the standalone watch setup. The Sony Smart Watch 3 is the only android wear smartwatch that doesnt required the software to have a patch installed. Have a look into this