I've tested the hypersync with my White Lightning x1600's in the past with some degree of success using the Phottix Odin triggers. The Odin TCU has the variable timing feature that allows you to dial in a specific timing offset for this very purpose.
I'll try to dig up the spreadsheet and sample images tomorrow to post the results here if anyone is actually interested, but there were enough issues with this technique that I've never actually tried to employ it in a real world shoot. The biggest problems were that the exposure was quite uneven across the frame, requiring a gradient exposure correction in LR to even out the frame in post, and the fact that the exposure varied unevenly with the power setting and shutter speed, with lower power settings being more effective than higher power settings. This obviously negates the effectiveness for outdoor daytime use . The other gotcha I remember is that the 1/4 power mode on the x1600 was virtually useless for hypersync. Oh and to top it off, I seem to remember this technique being more effective with my 7D than my 6D, so that's one more variable to consider as well.
TL;DR; Stick with ND filters and save yourself the hassle, or pick up one of the newer HSS-capable studio heads for this specific purpose.