Sound like experiment time.

The pdf that opened for me did not list any urea as a source of nitrogen. They have overloaded it with ammonium sulfate though, that's the problem since you can't take it out...so it is out of the desirable range for hydro in into the iffy zone of toxicity and lots of sulfur would also result. Not worth adapting this. It could be, but then it would end up costing more than other options.

You could try this fertilizer in something like 9g fert / 12g calcium nitrate / 10g epsom salt and see how it goes (since it doesn't look great I'm just guesstimating it, but that would be close). It is too light really on iron for lettuce and in this mix of only 9 g of the micros in general, so supplemental iron chelate would help with a tiny pinch of borax. For every gram additional of fert you would subtract one of calcium nitrate roughly but the resulting mixture would get toxic quick.

I goofed on the urea, ammonium sulfate was what had me concerned.
I can just buy the mail order stuff, I was just hating to pay that 20.00 in shipping.

The jacks I am looking at is the hydro feed in the upper right hand colum of this page http://www.jrpeters.com/Products/Hydroponics/Buy-Hydroponics.html

Here is a link that might be useful: http://www.jrpeters.com/Products/Hydroponics/Buy-Hydroponics.html

SouthernAg, Jack's hydro, Masterblend, will all will work fine, except the lettuce formula you had before is better as the micros in the big three are not made specifically with lettuce needs in mind so a commercial grower would notice a difference in yield for many varieties.