If your problem is enmity and not damage, I'd like to recommend just Overpower. It's what I do when I feel like I'm lagging or I don't have a pre-built SS/BB. I've tried Flash but it's honestly too much effort to get down the timing (Shadows spawn really slowly) and OP will seal hate against anything as long as you hit it as soon as possible. Mash tab target like your life depends on it (or, well, your WHM's life).

Another note, your WHM can either run next to you to hope and pray that they don't die from the single smack, or they can run away as the Shadow is coming toward them w/ Sprint and it'll leash back to you if you've gotten off OP/SS/whatever.