TBH I would delay implementing something you have not been frequently using especially given the potential to end up at tribunal because someone has been dismissed.

Most policies have sample refusal considered an automatic fail which given the hype and controls in the workplace about sterilising "touch points" would it be unreasonable for an employee to refuse to place their lips on anything handled by others?

I appreciate the Police are using breathalysers but it must be remembered they have been doing it for a long time and have a firm legislated basis for doing so.

what is the purpose of the testing? Is it with cause after an incident or simply a random test?  The more serious and relevant the reason then perhaps the more effort you might plan to put in pace on how its done.  You can fit the mouthpiece without touching it so you could set up the device and hand it to the person, assuming you have fully explained what you want them to do.  Of course if it is/was a serious matter and you don't want to go for a breath test, then have you look at the alternatives albeit they tend to be more time critical.