Unfortunately, we can't force users to do anything they don't wish to do. Furthermore, it isn't their problem. It's yours. It's up to you to make sure your site works on their browser/OS/device, not the other way around. You could encourage them to download another browser, but again, not their problem, yours.
That little bit wisdom out of the way, properly written code should have very few issues with IE. I really don't remember the last issue I had with IE that wasn't simple lack of support for something that wasn't expressly required. Does IE 8 support HTML5 tags natively? No, but everyone's aware of that, and simple javascript fixes it. Do 8 and below support border-radius? Background-size? Animations? Transitions? Nope, but it doesn't need to. If the base CSS is all valid and properly written, those users will see a gracefully degraded site that still looks good.