Yes, I've refreshed Shaw from Mexico, but I haven't needed to do it lately. I'm not sure if Shaw could/would block you with a non-Canadian ISP address. I have a Hughes internet dish through a Canadian Hughes reseller which probably has a US IP address (since some websites say I'm somewhere near Germantown Maryland which is where the Hughes sat station is) and there are many rural Canadians using Hughes, how would Shaw know whether Hughes users were Canadian or US?
I think that the concern expressed about Shaw and Canadians in the US is overblown. I had detailed E-mail and phone discussions with them before buying my Winegard auto dish, I told them I would use it in the US and I was interested in knowing how long the service on the two existing sats would last. They told me they couldn't support me down there but they didn't take any action unlike Bell did in the past.