Great news, we’ve just released a rebuilt version of the transfer tool, which adds this feature 
There are a number of other improvements (most around merging/splitting) in the new transfer tool, as well as it being more mobile-device-friendly. This update also opens the door for further improvements to the transfer process, such as (Automatically) Add ingredients/process aids/stock items during transfers between vessels & from brewing system which (along with the loss suggestion idea) have been held up on the tool getting a ground-up rebuild.
We hope this proves useful and I apologise for taking so long to complete this, especially when I appreciate that it looks simple on the surface.
Thank you 