What is insoluble in drinking alcohol, but edible?
Ethanol does not dissolve chocolate, which consists mostly of butter and sugar. These mini alcohol filled chocolates are very common party candies. You could try inserting one of these into your cupcakes after you have baked them.

You could also try making a mold for a gelatin-based shot cup, as gelatin is also insoluble in ethanol. Gelatin is capable of absorbing alcohol, however, so I do not recommend making these too far in advance, lest they turn soggy.