Simply choose 'Snipe' off the Share To menu when you are in an Item View page of the eBay mobile app, or an Item page on an eBay website, and it will open a browser tab pointed to eSnipe's mobile bid entry page. If you aren't already logged into eSnipe, they will prompt you to, and then forward you to their bid entry page.
DISCLAIMER: This application is unofficial and is not affiliated with www.esnipe.com or www.ebay.com