Buying Lightroom with a crappy internet connection and no disk drive?

I am traveling and will be for months, but I've got a new camera recently and want to buy Lightroom. Problem is, the internet connections are terrible and I have doubts that I can download it successfully. I have trouble enough loading web pages. The other issue is that I have a MB Air and it has no CD drive, so I can't buy a CD either.

I am with a friend with a PC who has a disk drive. If I buy the Mac version of LR, would he be able to transfer the software to a flash drive? If not, what would be the solution?