Small update here.
We have created ChipMixer plugin for Electrum. It allows you to tumble your bitcoins with us without leaving your wallet and it is even easier to use than website (prefill forms, creates new wallet and imports private keys for you).

You can check readme and screenshots here: https://github.com/chipmixer/electrum/tree/plugin/plugins/chipmixer
Pull request is pending, maybe it will get included in next version of Electrum.