Dear Augustin,
Thanks for the reference. I'll try to check it asap.
I'm aware that magic uses of various forms of the DN Yhwh were widespread (which was a rather logical consequence of its official sacralization and practical prohibition in monotheistic judaism). Just googled out the following article(s) as an interesting example among many: http://www.tfba.org/articles.php?articleid=4
However, the connection with Gnosticism seems more dubious to me. Magic is a popular practice which grows under the shadow of a popular religion, and I feel Gnosticism never really reached such a status, except in very limited periods and/or geographical areas. But that is just my intuition.