Honestly, I don't think anyone is going to let you monopolize the CPU on their server for that long (albeit it would take much less time on a server/cloud-based platform)...particularly for free. Your CPU usage is going to be restricted.
Secondly, you would have to find someone with a Windows server or Windows cloud (don't really know of any), with Excel already installed. Most servers and/or server platforms are not going to have Office installed. There's no reason to...just no reason for the expense. Perhaps OpenOffice could work, but does that run the macros? I have no clue.
Perhaps we could all brainstorm here and try to figure something out, but I think you might be out of luck. Anyone?