Here's an idea:
  1. Install lndhub on your node.
  2. Install bluewallet on your client's, pointed to your node.
  3. Add a lightning wallet on your client's bluewallets (they are pointed to your lndhub)
  4. Set them up on Kraken.
  5. Ask them to buy BTC via Kraken and withdraw via lightning to their wallet.
  6. Then they pay you via lightning to your wallet (which is also on bluewallet connected to your node). As it's a local payment fees are 0.
Good thing is that you become their banker effectively, and as soon as they withdraw from Kraken (and before they pay you) their money becomes part of your node's liquidity.
You'll just need a massive channel to Kraken with loads of inbound liquidity.