An oldie but goodie:
One of Cecil’s correspondents gives a solution:
Question: is this the one and only solution? Another possible way: if Batter #6 is batting out of turn, and hits the grand salami, can’t the opposing team appeal the play and nullify the runs? And wouldn’t the seventh batter still be standing at the plate when the appeal is made?
ISTM that before 1984, a “pine-tar” appeal would also do the trick. I know the rule was changed subsequently to George Brett’s famous incident so that the opposing team had to have the bat checked before or during the at-bat – not after – or the results of the at-bat stood.