This would have worked in the first 6 months of the war and should have been done then but almost all soldiers fighting for Russia in Ukraine currently are contract soldiers who are *usually* from the lowest socioeconomic rung of Russian society, signing up to fight for a few thousand dollars a month. You're just creating an even larger incentive to sign up with a defection bonus. And an even larger incentive for Russian commanders to throw their men into attacks they're unlikely to survive. Ukraine does pay out defection bonuses for those surrendering equipment, however Russia has gone to extreme lengths to target those who defected in order to deter it (https://www.bbc.com/news/world-europe-68337794).
Russia has for practical purposes an almost unlimited capacity to send people from its poorest regions to fight in Ukraine and take casualties at current rates. And somewhat counterintuitively as their economy worsens, higher interest rates, cost of living increases etc. that capacity increases because the pool of potential recruits who need that $4,000 a month or so grows. And it's not clear that people in the more prosperous regions of Russia have a strong view on the deaths of their countrymen, especially since they're "volunteering" for service in Ukraine unlike as was the case during their invasion of Afghanistan which utilized conscripts where casualties were a major reason for their withdrawal.
It's a tough position for Ukraine currently, and their best option is still the one that the West has sought to avoid all along, hit Russia in their pocketbook by targeting crude exports. Who knows, it's been primarily Biden who's discouraged long range strikes into Russia, maybe if the UK and France take the lead on things, that changes the calculus as they've been in favor of allowing them.