This is something I actually wouldn't be ashamed of drinking just because it has a nice level of alcohol in it!
Pretty much he makes a remix to the original recipe. Instead of pouring the alcohol in first or mixing it in with the actual fruit, he does this first. He mixes all the flavorings such as the strawberries, grenadine, and simple syrup. Then he pours the 1 or 2 of strong rum into the glass. After that, he pours the strawberry mix into the glass, so you get pockets of strong alcohol taste with the daiquiri. It's pretty cool actually! Check out the full recipe and steps;
2oz White Rum
1oz Simple Syrup