As you presumably know, the US generally doesn't treat transitting travelers any different than those whose final destination is in the US. I suspect that whether you get charged a customs duty will really depend on whether you get an officer who is inclined to look the other way (which can happen simply because the duty you'd pay is relatively small and processing it may be a bigger hassle than it's worth).

That said, two ideas: Worth shipping the gifts ahead to your final destinations? And is this liquor so rare that it can't be purchased in a US duty free shop before you depart for Canada?