You may ditribute the form as submission-enabled PDF form and then send out the PDF form out by email. Then use can save data and submit the form when he has internet connection. To save the form as PDF, go to "Distribute" tab and click on "Save submission-enabled PDF Form".
Thanks, this is the obvious answer and assumes that the person filling out the form has a PC.
The whole attraction of the "on line" (cloud) system is that regardless of the persons user rights on the PC he is using, or the memory, disc space etc. etc., he can still complete the form. We have guys, who have no PC and have to use a central PC, or indeed their own non-work based PC. Some are also using tablets with limited space and software. So this answer does not address these flexiblity issues.
Sorry that this alternative doesn't solve your problem but FormsCentral doesn't have a save on-line form data functionality currently. We'll consider your need in our future work. Thanks for your feedback!