For a solution you can implement today, you could look for an inexpensive/used Windows laptop. Many laptops have SD card readers built-in, but if you get one that doesn't, a USB adapter can be had for ~$10-20. Updating the 740's SD card via iFly Connect is very easy...I think it's easier than getting the 740 onto an unfamiliar wifi network and performing the update from inside the app.
As Brolin says, at least the first implementation of a device-to-device update solution will probably not extend to the 740 (he said "mobile devices only", by which I think he meant "Android and iOS phones and tablets"), so it's probably not realistic to expect such a feature to come to the 740 anytime soon.