And relying on non-existent (at that time) nationalisms like Belarusian or Ukrainian would piss off his really valuable asset - Poles, who could defect to anti-Napoleonic coalition (and it was proposed to Poniatowski by tsar Alexander multiple times), so why Nappy would try to actively lose his only valuable ally inside the empire in exchange for...nothing? Because Belarussian/Ukrainian peasants were neutral or pro-Russian, so no support from them, and supporting them means losing only group actually willing to support him. I think better plan to improve Napppy's shots at winning would be actually listen to Józef Poniatowski and go south, to Ukraine - climate isn't as harsh as in central Russia, more Polish presence means more collaboration from locals and there is always a possibility of wooing Turkey into alliance.
The main problem with going South is that it does not achieve any strategic goal as far as Napoleon is concerned. Polish influence on the Russian part of Ukraine was quite weak by 1812 and attempts to “restore” it (which was probably Poniatowski idea) would met the local resistance.
All these alternative speculations are completely ignoring Napoleon’s main strategic goal. His purpose was not to restore the PLC or to partition the Russian empire. As far as I can tell his main goals were to force AI to reinstate the CS and to prevent him from making noises about the “imperial” affairs (*). Nappy’s idea how to achieve this goal was simple: to destroy Russian armies close to the bordering expectation that this, as happened earlier, would force him to start talks and agree to Nappy’s demands (Tilsit #2). On the 1st part of his plan he was not unrealistic because strategic plan proposed by general von Phull and adopted by Alexander would result in the Ulm-like situation for the Russian 1st Army. Even after this plan was abandoned due to its obvious idiocy not everything was lost for Nappy because the “Russian party” in the army led by ...er... “truly Russian” (actually Georgian) Prince Bagration was itching for a major field battle no matter the odds (**). But after Barclay refused to fight a decisive battle at Smolensk (to be entrapped and destroyed) Nappy’s chance was totally gone.
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(*) The talks preceding the war included on Nappy’s side the following subjects: revocation of tariff of 1811 which he considered personally offensive, revocation of Alexander’s declaration regarding annexation of Oldenburg, an issue of the Russian military concentration on the Neman and acknowledgement of Napoleon’s right to move as many troops as he wants on the territories of his allies. The sticking point was the last issue.
(**) This was a part of “Suvorov’s heritage”: quite a few Russian generals of that period tended to disregard the opponent’s numbers on an assumption that an energetic bayonet charge is going to solve all problems. This already backfired during the Finnish war when Russian commander in chief sent a corps of 4 - 5,000 against 12 - 14,000 Swedes with the orders to attack and chase enemy away.
