You could use something like an Arduino to buffer
either. It could take the 9600 from the terminal and
retransmit it at 110. It would be slow when updating
data to the terminal but it should be able to buffer human
input at the terminal.
If you're going to keep the PDP11 port at 110 baud, then
you might as well just turn the switches on the VT52 to make
that do 110 buad too and use a 4 pole changeover switch to
select between the 2 terminals.
Why use a million components when a couple will do?
-tony