A piece of 25mm wide elastic (black doesn't show the dirt), and the end section of any lanyard that has a ring/clip and one Acme Thunderer whistle.
Wrap elastic around wrist so it is comfortable i.e. not stretched, and cut to length allowing an extra 25mm for over lap.
Attach whistle to lanyard and hold in normal position as you would during a match and lay lanyard across palm, down wrist to where elastic will sit and mark the lanyard. Allow an extra 50mm so that cut end of lanyard can go under the elastic and double-back on top of elastic. Pin lanyard to elastic in final position and hand it to your wife with, "Be a champ and run this through the sewing machine please luv?"
If you make two, you'll have time to have a coffee, a beer or maybe even a glass of your favourite red.
Can post pic if needed. Best whistle lanyard.
Alternatively, steal one of those rubber bracelets from your kids and a lace out of one of their school shoes and copy Chris Pollock's design.
Cheers.