Hi cfrith5,
If you want to, just install the program on both your computer and your friends in San Diego. I have it installed on my desktop, laptop, and my daughters laptop.
As cemeb4dk said, the online version may be better for saving your plans, but I've always got better results with the download version. Plus, I tweak the final results like crazy and end up with my own fairly customized plan to avoid crisscrossing the park for FP's and also so I can run for FP's while my family rides some rides I don't mind missing - this may or may not be ideal for you.
I would suggest trying both, try the download version before you leave and see if you like it better than the online version. If you end up preferring the download version, just install it on your friends system when you get to SD.
Good luck and have a great trip!