Actually your idea is not that great because fiat currencies from Western countries are next to worthless to Russia. The USD, Euro, Yen, etc Russia Central Bank receives are of little use because of the sanctions. All the new Rubles will flow back to Russia as payment for the fossil fuels and will lead to inflation because of the extra money supply, unless the Russia central bank soak them up.As for keeping Rubles in Russia's current account, I assume it's referring to the BIS; in which case it makes no sense at all. If foreign countries need to buy rubles to pay for Russian exports, they would do so either through other countries with excess rubles to sell or buy from Russian central banks via commercial banks. If it's through the Russian central bank, it can simply "print" rubles and in turn earn foreign currencies which can be used to pay for imports or buy foreign assets. The "printing" in this case is supported by the exporting so it's not inflationary. There's no need to keep rubles in its current account as reserves.
Another method for countries to get Ruble/RMB is to issue bonds in Rubles/RMB and are bought by Russian/Chinese Central Bank. Russia and China will be providing other countries fiat moneys to buy their products (fossil fuel from Russia and consumer and industrial good from China). Same as above, the result will also be inflationary because the new money will go back to Russia and China, unless their central banks use money market operations to soak up the extra liquidity.