So, the short answer is:
If you have to bastardize it to use it, you're doing it wrong
I get that we're a culture of hackers, and makers, and tinkerers, but you have to appreciate that the site isn't for your benefit, it's for the benefit of others. It may look cute to you, but it may actively disrupt the ability of others to use. See "not all browsers support unicode" and "not all unicode will be displayed with your choice of font" and "screen readers may actively mispronounce what you're saying because you're doing the wrong thing" all of which mean "the user doesn't understand what you're trying to impart to them because you were being clever.
Don't be "clever".
Also of note is that the SE team has invested many many hours in design and research, and in a consistent user experience across the entire network of sites, and the discussion even amongst the User Experience Gurus on the UX Stack Exchange Site have already addressed your question here: Is there ever a requirement to allow text to be underlined when it's not a link or a header. Not only has SE invested a lot of time in it, they've hired experts in UX to ensure that the site is highly functional for all users. So by doing this, you're subverting the knowledge of experts.
I assure you had the UX experts said "no no, we really need to have underlining" that the SE devs would've included it.
So again the short answer is:
You're doing it wrong.
The internet at large would appreciate you being less clever.
But the maker-hacker-clever-tinkerer in me loves it. :D