When you allow less common tools to be used, one could use the bash or zsh read-builtin to read the master password without echoing (e.g. dash's read can not do

When you allow less common tools to be used, one could use the bash or zsh read-builtin to read the master password without echoing (e.g. dash's read can not do that) and use xclip or similar to directly put the password into the X clipboard. With xclip's -l option you could even automagically "forget" the clipboard after it was pasted once.