That is not an easy one. There really is no simply way that I know of unless you have someone in Europe or elsewhere you trust.

The thing about BNB is there is a pool on CubFinance. Hence, you can get it with either CUB or bLEO. Thus, if you can get onto the platform using LEO, then you can do it.

Simply convert LEO to bLEO using the directions outlined in the docs on the Cubfinance site. Once you have bLEO in your wallet, you can use the exchange button to swap it for BNB.