The thing with that song if you'll be playing the riff on one string anyway, no? - you shouldn't necessarily need to be muting the other strings.
I'll only really mute other strings during lead paying with bends if I want to play aggressively by raking muted strings along with the bend...or if i'm playing some lead that is played on multiple strings at speed, then id probably use some light palm muting to keep it a bit more defined and cleaner.
I can't really understand why Wonderful Tonight would need any muting, it's a fairly slow riff and played along the B string. As long as you're picking accurately and nicely, there shouldn't really be any need to mute other strings and they shouldn't be ringing or being touched for that riff. If you need to be muting on that riff, then id say you probably need to be more careful with your pick hitting other strings, or be careful your fretting hand isn't causing the other strings to ring out when you bend the note and your fingers brush the other strings. If you're doing that right, then you don't need to be palm muting that riff