Well I am willing to give it a shot, how would I go about finding a schematic?
It's fairly simple, miminum would be two parts, the diode and a cap. The cathode of the diode (usually marked with a band) connects to the + voltage input of the DC voltmeter. The anode of the diode goes to the voltage being measured. The cap goes between the + and the common of the DC voltmeter. The common of the voltmeter also goes to the ground (or other end of the voltage being measured). Now to select the diode and cap: What is the highest voltage you will ever want to measure, or will be present in the area of where you will be poking around? You want the diode to not blow up. Minimum voltage rating "peak inverse voltage" needs to be at least 2.8 times the RMS (assuming a sine wave) voltage of the AC voltage you will measure. The cap should charge up to drive the meter but not hold it too long once you remove the probe from the voltage your measuring. Say 1/10 second. If the DC voltmeter has a load of about 5 megohms, the cap would be 0.1uF to 0.02uF. Its voltage rating should be higher than 1.4 times the highest RMS voltage you will ever measure. I'm thinking out loud here and haven't tried it, but this should work. Try measuring some voltages of known peak to peak voltage to test this out first.