Read-only Shared Access

While the new Shared Access feature is really a nice and cool feature, I cannot understand, why there is not a button to limit the access to read-only. 
I often want to share and show my account to other peer traders, BUT I DO NOT WANT THAT THEY  CAN TRADE ON MY ACCOUNT!!!

PLLLLLLLLLLEEEEEEEEAAAAAAAAAAAASSSSSSSSSSSSE add a read-only button!!!