I know you said you tried one with olive oil and that it was way to strong. But here is my idea:
2 egg yolks
1 -1.5 cups Olive Oil
1/2 tsp - mustard powder
For the lemon juice I would start with a squirt and then add to taste but probably no more than half a lemon. Add salt and pepper to taste. White pepper is purely for aesthetics, but if you aren't opposed to black specs go with black pepper. And for the olive oil, try using virgin olive oil or just plain olive oil. Stay away from EVOO, as you said it's taste is to strong and over-powering.
Whisk egg yolk, mustard powder, salt, and pepper together. Add half of lemon juice to egg mixture and whisk. Now here comes the forearm workout. Continue whisking the egg mixture and begin to slowly add the oil a little bit at a time until it begins to thicken. It should also begin to aerate a little as well. This means you have successfully started to emulsify the ingredients. Increase the pour of oil to a steady stream, after half the oil is incorporated add the remaining lemon juice. Once all the oil is incorporated leave it for a few hours. Should last a week or so in the refrigerator.
Or if you want to do it the easy way just do it in a blender. But remember to add the oil slowly.
I am not sure about using coconut oil, could be interesting. I imagine it to make a sweet mayonnaise. Also I thought about tahini? Not sure, just an idea. As suggested you could mix 3/4 cup flax oil and 1/2 to 3/4 cup olive oil.
Brad, if you ever want to start up a Paleo food company let me know.