Seeing as how you waived your right to councel, Mr. Shelton, Do you have anything to say?
"Seeing as" is a paraphrastic (how about that for a word?) way of saying "since" -- a little like "is going to" for "will".
as = expletive?
a word or phrase conveying no independent meaning but added to fill out a sentence or metrical line
"seeing as how" is the whole paraphrastic "since".
I guess "as" could be considered an expletive, but I don't think of it that way.