I use invisible thread for attaching beads and for finishing ornament edges, especially when I'm using a lacy ribbon for the edging. It's kind of a pain to work with, being so barely visible, but the end result is fantastic! Never thought of using it as sort of a blending filament... would go with a Kreinik for that. Interesting.
p.s. Nordic Needle sells YLI also... might give them a call, though their standard shipping is high.