It should still be possible to compost the entire pile of grape pomace. It may be beneficial to add manure to the pile to introduce microbes that will re-invigorate the decomposition process. You will need to be sure to turn the compost pile frequently to aerate it. It will also help to hose down the pile occasionally to provide moisture for the composting microbes. As you stated, it will be best if you use the compost on the marginal parts of the property, as it will not be commercial grade. I’ve included a link to our article on building a compost pile: