I live on an island in SE Alaska; I expect my climate is very similar to yours.
I have not messed with food plots, but as far as what will grow, you are right- corn won't. A few folks do grow it in a greenhouse here, but it won't work outdoors.
Clover was planted by the forest service as a cover along logging roads at one time here, several different species. They seemed to do well, I still see it growing in patches where they tried it.
A lot of gardeners here build up the soil with drifted kelp gathered at the high water mark on the beach. Just take a skiff ashore at a good spot and fill the boat, then trailer the boat with the kelp in it. Wood ashes and ground shells from the beach are also useful depending on your soil test results.
There may be some issues about introducing species into your area that will come up. Something to consider beforehand.
If you follow through, please post the results.