How far away is the closest office to them? Goa to Mumbai would be way too far, but if they're an hour away, it may be the most cost effective route to have them come in to that office.
Do the employees go to any office normally? Or do they work from home? In either case, an IPSec VPN from their firewall/router to your firewall would produce good results. But it'll take a long time to set up a VPN for each individual employee/router configuration. It would be best if they all congregated within a few buildings or other employee's houses for the procedure.
A third option would be to mail them all new laptops already configured and set up. I did this for one client, and it was the easiest way I've ever done it, but it was the most expensive route. It's worth investigating if the company is looking to upgrade to new laptops though.
Something that is not an option: doing this across the Internet without a VPN/tunnel. For both security reasons, and the likelihood it wouldn't even work.