Pop-up IFR from Clearance Delivery

Andrew Sarangan wrote:
Let me clarify the question. On a VFR training flight, we encountered
unforecasted ceilings of about 1500'. So we landed at a nearby
uncontrolled airport. There is no RCO to FSS. In order to call FSS we
would have to taxi to the ramp, shutdown and find a telephone. But
there was a remote communication outlet to the nearby class C
clearance delivery. So we decided to call them instead. They asked me
to file with FSS or call them (Approach) when airborne. So we departed
VFR and got our clearance. My question is, why could't the clearance
delivery guy give us the same clearance? I realize that the proper
procedure is to file with FSS, but what prevents CD from giving a
pop-up clearance?

The same thing that prevents ground control from giving you a takeoff
clearance. He could but he is not responsible for that position.
That's why FSS says "ATC clears..." when they relay a clearance to you.
That's how you know that it wasn't FSS that actually made up the
clearance.