I don't know about any software solutions, but you could make your own little current sense circuit in hardware simple enough if you're willing to go that route.
I really like "these current sense amps":http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=SC310BSKCT-ND as simple to implement high side sensors for the purpose of measuring input power in a lot of applications.
For any such application go through the basic checklist:
1) Make sure you are within the upper and lower limits of common mode voltage range for the IC (or the measurements become too inaccurate).
2) Choose an appropriate current sense resistor for the current range you wish to measure so that you use as much off the effective differential sense voltage range as you can.
3) Add a couple of scope probe test points for the output voltage of the amp (current) and input voltage of your circuit downstream of the sense resistor.
With those things, two scope probes, and effective use of the math functions of most oscilloscopes you can get pretty good samplings for a plot of "continuous" input power for many applications. Even without the necessary math functions on scope, if you can capture the two plots as data on equal timescales and port them to a spreadsheet then you can do the math there.
