Related Clues:

• Stick a cat in a hat up here
• Stick a teetotaller on the start of 13 across
• Hook up with a non-drinker, alas in Berlin
• Attach a really loud 1-across?
• Add-on to the start or end of a word stem (as in 17-, 25-, 35-, 49- and 57-Across)
• Append return of 'The Cat in the Hat', perhaps
• Fix to short handlebar, say
• Join in a fortissimo number
• Fasten - assign
• Fasten - attribute
• Join onto
• Join in a very loud number
• Add to an e-mail, as a file
• Send with an email
• Couple to race in motoring organisation to Switzerland