I roast a small to medium whole goose in the oven hotter and for a shorter time than for a comparably-sized domestic goose, about 325 F for about 1 3/4 hours. Domestic goose can bear slow cooking to overcome its toughness, but wild goose is extremely lean and slow cooking can dry it out. For a big goose, you might want to carve it first for more even cooking, but the table presentation won't be as nice. Unfortunately, I've never been able to get enough drippings and blood for decent goose gravy, which would be nice with roast whole bird.
The best thing I have done, though, is to smoke the bird. I carve it first then use a propane smoker (and, heck, after all the money you've already spent, she's not going to get on you for spending $250 on the smoker :). Give it all the steam you can but use a little less wood chips than you would use for pork cuts or brisket. Charcoal would be harder to manage, but it would not create an inferno as chargrilling fatty domestic goose would. Shoot for around 300F for 2 hours.
I don't marinate it, just rub it with salt, pepper, oil, and garlic. In the over I sometimes put rosemary sprigs on it. Either way, while rare-to-medium wild goose is delicious, I'd recommend cooking it thoroughly d/t unpredictable parasites and microbes in wild birds.