I have seen a couple small parts online that look like they may do the trick.
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http://www.boatersworld.com/product/366790038.htm?bct=t13046503%3Bcimotor-engine-systems%3Bcifuel-systems%3Bcifuel-hose-accessories Attwood's fuel vent line surge protector helps avoid refueling spills because the surge causes automatic fuel nozzles to shut off as the tank fills. Meets ABYC Standards. Glass-filled polypropylene construction and surge-ball design. Installs in-line with traditional 5/8" I.D. vent hose tank systems. Withstands oil, gas, and alcohol-blended fuels. Compact size allows installation inside gunwale in any orientation within 45 degrees of vertical. Includes two hose clamps.
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I also saw something that made noise or chirped when it got closer to being full. Couldn't find it right now sorry.