It’s possible, but I wouldn’t do that, as those polls are not directly comparable: respondents are not given the same choices, so the underlying probabilities differ.
Something you could do is use masking to force the option that’s not there to have zero probability – e.g -999, which is gonna turn into 0 when you softmax everything to get the vector of probabilities. It’s what I did a few years ago in the presidential model I linked a few posts above, IIRC.
You can also always use two different likelihoods in the same models if that’s easier for now.
Hope this helps 