Good point, actually I was also v14 for WMII. I wouldn't put much effort into leveling the unlabored blade with a rogue until at least picking up Deathblows at lv11.
As it was when I hit groups of 3+ I would use a cross bow to get a runner's wounding shot or hobbled to get sneak attack bonuses rolling faster and put off using up Shadowing Beyond and Killing Blow as long as possible.
If I wanted the unlabored blade leveled even faster or any soul bound dps based req in a tougher situation I guess I'd just cut out other sources of dps in the party.
So in my last party I'd first try keeping Aloth's crowd control grimoire on the case and bringing in an extremely tanky unenchanted larder door wielding Eder soaking up aggro, adding a steady flow of low dps knock downs
Whatever works in your group to get that 2000 or so damage in without too much hassle!