Here is a reference which slightly predates Wotton:

Who can be sure of the first person to apply the split-thread technique? I know of several for whom I havedemonstrated it that indicate they have seen it before. Gary Kaplin sent me some written material from aclass Steve Gobin taught in San Francisco in 1992. In it Gobin tells how he uses a bodkin to split thethread, then "wax lightly and rub your dubbing down to lightly dust the thread with fur. Close the loop andtwist counter-clockwise." The technique is bound to have been around for some time, though I am surprisedthat I have not seen it before. Split-thread dubbing was first brought to my attention by Davy Wotton ofWales when I visited
with him in May, 1994.