Which conductive ink would you recommend?

I couldn't find the thread with the pics, though I vaguely remember it. The silver trace pen you have a link to is good. However not the best option for fine work, but can do it with a "form". It will "pool up" somewhat as you mentioned with the glue you are using. What I suggest you do is take tape and put it on either side of where you want the trace to be. That will make a controlled channel for either the glue you presently have or the material from the trace pen to reside in. By doing this you can get your trace from a to b and control c. Leave the tape on long enough for the substance to just start to get tacky, but not dried yet, and pull the tape up. That should leave your trace from a to b with no c.

Added with edit:

I would solder a fine single strand wire to the trace and rebuild the solder pad. Here is the main solder I use. Most armatures can get a professional looking solder joint using this solder paste. It melts low profile on the metal. The gist of my review there says this about the product: It is a great low heat solder paste, melts at approximately 183 °C (361 °F). The metal content by volume is somewhere around 90%, based on the character of its performance. It has great viscosity. It sticks where you put it. The product consistently produces a strong, neat bond with low heat.

I would scrape off coating from a small section of the existing trace. Then apply a small amount of the solder paste to that area and hit it with the soldering iron to tin it. Then rebuild the pad with a small piece of copper foil cut off a copper pot scrubber. I would apply a small amount of the solder paste with a toothpick to both ends of the fine wire and the new pad. Then hit them with the soldering iron to tin them, also. Then use a small amount of the paste at each joint to tack them all together. The thin piece of copper wire I would get from a section of multistrand wire, just 1 strand. After everything is in place cover the new trace up it a couple of coats of clear finger nail polish, to keep it in place and to ensure that it remains in place and can't short out.

I do this for a living. I have multiple soldering stations, with multiple tips for each of them. I have a stereo microscope that zooms to 90X to work under and inspect the work.

I have used the trace pen you refer to on a number of occasions for various things. I have even used it with the tape as I previously described to mend the flex cable on DS Lite upper screens. One of the main things you have to watch out for is the tip tends to dry out quickly. After the tip dries out the pen is useless. So you will need to get all your projects finished within a few days.