I have Ed Rosenthal's 'Marijuana Pest and Disease Control' book here and he has a number of strategies to deal with root aphids.
Good old neem drench.
D-Limonene citrus oil.
Azadirachtin, an alcohol extract of neem.
Herbal oils. (whatever that means)
Pyrethrum as a soil drench.
For bio controls he lists,
Beauveria bassiana. A fungus that can control over 95% of root aphids.
Beneficial nematodes. Good against aphids, fungus gnats and thrips.
Spinosad.
Nothing about how much of each stuff you have to use but shouldn't be hard to find out.
Hope that helps and you get rid of the little demons.