And for good measure, Ukraine should "sell" its ownership in the Ukrainian section of the gas pipeline to a Nato country and then shut off the flow of gas.
Cutting off the flow of gas would hurt Europe a lot more than it would hurt Russia at this point. Entering the winter with your largest gas supplier no longer providing you with the gas that you use for heating would suck. And as gas is fungible, it doesn't matter to Russia if we stop buying it from them, unless everyone else stops buying it from them - if China doesn't join in with the boycott then it just means that they'll be buying more has from Russia because the price of everyone else's gas will go up.
No Russian economy depends on this income, it make up a significant part of their entire national GDP, meanwhile Europe has been finding other alternative sources of energy in case Russia would cut of the supply again as they did after the sanction put on them for the invasion of Georgia. And the gas is not fungible, it would take over a year to build new pipelines to other countries, especially China is a long long way away from the gas going to Europe. Russia would be completely and utterly fucked without the gas, in Europe it would just hurt the home owner who has invested in natural gas heating to save money, they would not be saving money anymore.