I have literally never hesitated to turn on my system. If you can’t afford new tubes, spend less on groceries.
and obtw, the architecture of a passive pre it totally different. You are asking for 2 totally different components.
Tube Preamps Should Have This Feature
So it's late or you just want some casual listening for a short time. "Should I fire up my tube pre for 30 minutes?". My answer is "No". Why not let me flip a switch (or push in the volume control) to put my pre into "bypass" mode? Bypass would, effectively, convert your pre into a passive device, keeping the tubes dark.
This sounds useful to me.