Unfortunately Anchor does not give podcast creators the control and ability to add analytics prefixes to their Anchor RSS feeds.
Since many other hosting providers do support the Podcorn prefix without issue, we hope that Anchor will be able to accommodate your request in the future.
Good news though! You can still use Podcorn to find sponsorship opportunities. You will just need to share screenshots of your show's analytics in your proposals, since Podcorn won't be able to verify your analytics automatically.
Anchor does provide a useful metric called Estimated Audience Size that is based on the average number of plays each of your episodes get in the first 30 days after publishing, so take a screenshot of that number in your Anchor dashboard and share it in your proposals to sponsors.
You can also share a screenshot of the total number of downloads your show recieved in a recent week (see the Plays metric in your Anchor dashboard and select the weekly view). Learn more about Anchor's analytics here.
Additionally, including audience demographic information (like what you can get from Spotify) will help increase your success rate for proposals as well, as it helps the sponsor determine if your show and audience is a good fit for their campaign.
Once you complete the sponsorship and publish the approved content, brands will likely ask for a 30-day download count at which point you can provide a screenshot of the downloads that the episode got in the previous month.
To learn more about how to get sponsors for your podcast, check out: