That would work great for half an hour, until your Bluetooth connection drops for no reason, the dongle pairs with your car or phone instead, decides it's a headset now, or one of the hundred other things that inevitably go wrong with Bluetooth.
hehe, Do not think like an engineer in this case. Think like someone who only has to get it right once but can try 100 times. So even if you have a flake connection. Just so long as it works that 'one time'. You are good.
A phone could work. An apparent car key would be better. Best would be a piece of clothing, like a belt.