This can be accomplished by introducing adapted nonterminal rules: in a revised generative process, the author can draw from Pitman-Yor distribution whose base distribution is over word sequences of arbitrary length.
4 in a setting where, say, K = 2, and our two classes are PROGRESSIVE and CONSERVATIVE, the sequence health care for all might be generated as a single unit for the progressive perspective, but in the conservative perspective the same sequence might be generated as three separate draws: health care, for, all.