I put a bounty on my question and I found the answer (or at least led me to it) in another question. Can I send that person the bounty?
However, if you really want to award that answer on the other question, you could start a bounty on that question. Choose the "reward existing answer" option. Wait 2 days, and give that answer the bounty you placed.
For more info on bounties, read the bounty FAQ.
@curiousdannii came up with an interesting idea that may just work in some cases. Raise a custom mod flag and ask for the other question to be merged to the question you placed a bounty on. However, they must be exact duplicates and no guarantee a mod would merge them or the way you want. However, not sure if this technique has ever been used in a case like this before, so can't say if it would for sure work.