Found a good method that may work for you:
"Here's a method I have used for finding exact TDC that does not require any fancy equipment. Remove the glowplug (and not the injector) from either #1 or #4 (#4 works easily for this). Rotate the crank until it is rising on the compression stroke for the cylinder. Then use a length of clear tubing pushed into the glow plug hole. Make a good seal around it. If necessary, use grease or sealant. Then place the other length of the hose in a container (preferably clear) of water. Rotate the crankshaft slowly and you will see bubbles coming out of the tubing. At exact TDC, the bubbles will stop moving out of the tube and water will start being pulled in."
From
http://vwdiesel.net/forum/index.php/topic,46544.0.html, post #8.
NOTE: Cylinder #1 will work best for us. Poster libbydiesel suggests to use #4 because on the VW 4-cyl, the IP hinders access for #1.
Then you can epoxy a suitable replacement indicator to the bellhousing for the missing triangle indicator on yours.