I could do this for you since I just received the amount of ethereum in my wallet of $2.58 (so can do this not including the sending fee of $2.50) an hour ago. Was just about to send it to another site. So good timing on your part.
But dont know what a mixin messenger app is and how to use it.
Wouldnt I just be sending the ethereum to your address and you sending the btc to my btc address?
This would probably be the best thing to do.
Nope not like that, i cannot sent or transfer this funds on your btc address you need to have a mixin messenger app to be able to have free without fees.
Would the ethereum be sent using the mixin messenger or would you want that sent to your own eth address so not to pay any fees to withdraw from the app?
I will see if I can install it tomorrow cause it looks as if you need some sort of verification (pin by phone) to use it.
This I do not have unfortunately.