What John Kirkpatrick wrote, nearly forty years ago, was:

"...hit the button quickly and take your finger off straight away. This will give you a loud, clean note and is the sort of procedure you should bear in mind if you want to produce good dance music... One exercise which helps strengthen the fingers and therefore makes this staccato technique easier to perform is to tap each finger separately as quickly as you can and for as long as you can bear to on any hard surface - a chair arm or table or a friendly knee - and develop the hammer action involved."

It seems pretty obvious to me that what JK was talking about was not 'strength', but the ability to make rapid, repetitive movements of the fingers involving both the adductor and abductor muscles working alternately. I must admit I've never felt moved to do it, but tapping them on a table seems a reasonable suggestion for enhancing this ability, and something that could be done at any time, whether or not an instrument was available.