the whole thing about the waste in your pee is basically 2 things:
1. the things your body can't absorb in food/supplements will be removed from your body through kidneys and subsequently out thru your pee.
2. the things your body needs to expel as waste (bacterium, lactic acids from muscles, cellular waste, etc...)
drinking milk is good for you. easily absorbed calcium in proper format for your body. you probably won't have much calcium excess as waste drinking milk. the multivitamins work better as the molecules aren't as easily absorbed by your body (hence the concentrated amounts, the manufacturers know you won't be able to absorb the entire dose - that's why they are "supplements" to a proper diet.) and a LARGE percentage gets removed thru pee. though the molecules of the vitamins may not be the ideal format for the human body, after passing thru the body, it is in a good state for breakdown in soil and subsequent absorption thru plants root system (not sure about foliar spray, so don't quote me on that, but if you're already doing pee foliar spray without adverse effects, i would say give it a shot and keep an eye on it..
might be that buildup on the leaves might be problematic if concentrations are high? that's my thoughts on it. maybe more dilution required for foliar?
you can get magnesium into soil far easier with a tablespoon of epsom salts... though i don't think you should sprinkle that on your popcorn and eat it...
again, if it's about making fert with your body, skip the rolaids and do the multivitamins. you'll get much more bang for the buck that way.
calcium, magnesium, iron, b, c, d, e vitamins, zinc, copper, potassium, silicon, manganese, phosphorous... pick up a bottle and read the supplement facts. everything you're looking for in a good fert is in the multivitamins. ESPECIALLY the "trace minerals".
i would also think you'll get pretty constipated drinking milk and munching rolaids. :O
don't advise.