Rerouter,
You have some ideas that can work, but you might be over complicating things.
First though, if you use a single LT3080, then if you want to output to go to over 30V, then you will have to reduce the current to about 250mA. Alternatively, you parallel 4 LT3080's at the cost to a slightly degraded voltage regulation due resistors you have to add to the LT3080 outputs.
Which way were you thinking of going?
Now Dave had some very particular design restrictions, that meant he absolutely had to be able to run his design from a single supply. 30V+ output sounds like you have a transformer, and once you have a transformer, getting a low current negative supply only costs some cheap diodes and capacitors (even if the transformer is just a single winding) and perhaps a 79L05 regulator. It would be nuts if you can have a negative supply, to not use it. You get much better regulation even at 0V out, the current source fed from the negative rail can sink down to 0V without any problem, you can use easy-to-get LM317's instead of LT3080, since you can offset the control voltage by -1.25V. A rail to rail opamp trying to work at 0 V does not work as well as a standard opamp with a negative rail working at 0 volts.
I haven't looked at the specs for the A/D. Does it need to be driven from a low impedance source, or can you add a series resistor to the op-amp to limit any overvoltage current?
Richard.