Potted citrus companions

I have a Bearss lime in a pot that has been plagued with scale (and therefore, also, sooty mold) since it came to me. My goal this year is to put an end to it, once and for all. My plan of attack is to continue spraying with insecticidal soap through the rest of the winter and then in the spring I'm going to spread a nice thick layer of Vaseline on the top of the pot to keep the ants out. I will be planting some alyssum and yarrow in pots that will be kept right next to the lime tree's pot. My hope is that I attract so many parasitic wasps this year that the scale doesn't stand a chance.

I'd like to also plant something directly in the tree's pot, but I know that resources are at a premium whenever you stick a plant in a pot. So, my question is, should I even bother putting something in the tree's pot? And if so, would something tap rooty, like parsley work best?

Thanks!