There's an appnote on using the tlc5940 with mosfets:
Is this the path I should be taking
No this is for using the TLC with a higher VOLTAGE supply. You want to make it drive higher current.
Stick with what you said before, substitute a resistor for the LED and use the voltage at the chip to drive a transistor or FET.
I'd rather not have to solder 48 transistors
Sorry but if you want to control 48 channels of 700mA each that's what you will have to do.
A 2N2222 is cheap enough and will handle buckets of current especially if you use a heat sink. Otherwise a hex fet would probably not need a heat sink, have a look at those.