Mixing Dash is actually very simple.

1) Sell Dash for XMR on Poloniex
2) Send XMR to own XMR address
3) Send XMR to a second XMR address with a mixin of say 5
4) Sell XMR for Dash on Shapeshift.io

Voila! Mixed Dash. No need to wait for weeks or worry about masternode blinding.

Edit: When sending the XMR to Shapeshift.io also use a mixin of say 5