Maybe, but color me unconvinced. Russia can,and did, play the Panslavism card without needing to create a Polish entity. St Petersburg carving up Russia for propaganda's sake after four years of conflict sounds rather unlikely to me as well. It would be a bit like France setting up an autonomous Alsace Lorraine in 1918 and giving it Belfort to its new client state.
They are not really carving up Russia, but rather letting Poland have the appearance of independence mostly at German and Austrian expense.