Wouldn't mix it with the nutes....urine is strong enough to use as a nute in itself. An example of a decent schedule would be alternating...on one watering use reg nutes, next use urine, the one after that just give a thorough watering where you see the run off coming out a bit (don't let the plants sit in filled catch trays)...rinse and repeat. Also, make sure you rinse off your catch trays once in a while. Salt from the urine will build up on them and your roots could end up being exposed to concentrated run off salts.
You could also run an experiment if you wanted to...feed some plants only urine, feed some only commercial ferts, and then feed some a little of both. That way you could find out what is best for you. Don't know if you feel like keeping track of all that though. Let me know how it goes!