Supra-supramaximal inspiration! An exercise that is 100% effective in treating hiccups for everyone who is able to do it (according to the one study we have):
First, exhale completely, then inhale a deep breath. Wait 10 seconds, then—without exhaling—inhale a little more. Wait another five seconds, then top up the breath again. Finally, exhale. Generally, you will find that your singultus is gone.
Works for me and my partner. Imagine if science had funding.