I haven't taken the time to read the whole thread, but you certainly CAN have varying NOT CHOPPED voltage (and constant current, too, if you have a current sensor in the path) with PWM. You simply have to make a 'buck' converter. You can find a schematic at

http://dl.dropbox.com/u/566712/PIC_BUCK.jpg

To be accurate, the circuit does require a small minimum load. You also have to measure the output voltage with an A/D channel and change the PWM value accordingly, but the output is a low-ripple DC voltage at up to 6 Amps.