STIR gin, Campari and vermouth with ice and fine strain into chilled shot glass. Carefully position the shot glass in the beer glass. Then carefully POUR Peroni into beer glass so not quite reaching the top of the shot glass, being careful not to splash any beer into shot glass. Instruct drinker to drink from beer glass and so inevitably also shot glass. Use sturdy glassware.
Negroni is a great chaser to beer so why not consume in unison.