Is it possible to set a bounty for an old question somehow?

I want to try my luck and see if someone can answer this question I made about a month ago: Simplifying the summation $(3^i\sqrt{n/3^i})/\log_2(n/3^i)$ from $i=0 \text{ to }k-1$

I thought maybe a good way to draw attention to the question would be by starting a bounty, but I came to the realization that I cannot longer do this. Is there a way to make the option be available again?