2 strands 4mm yarn on 8mm needles?

Just wondering if anyone can help me?
I’m a fairly inexperienced but enthusiastic knitter!
Found this gorgeous cutesy pattern::muah:
[SIZE=3][FONT=Times New Roman]http://zakkalife.blogspot.com/2007/10/knit-pencil-scarf.html[/FONT][/SIZE]
and i [COLOR=red]really[/COLOR] wanna make one for my niece and nephew for Christmas but i cant afford to buy lotsa new yarn right now!!
A common dilemma!!
I DO have vast quantities of 4 mm yarn that i got a great bargain on and that i use with my class (i teach 10 year old girls) so can i just double it up and knit on 8mm needles??

That’s a cute scarf, I saw it yesterday. But the needles it uses are US 8 which are 5mm. By 4mm yarn, do you mean that’s the size needle you would normally use? If so, you could probably do the scarf single stranded on the 4mm or maybe 4.5mm. It would be a little narrower, or you could increase a few more stitches. Like for the black, increase to 9, inc with the beige to 18, then maybe double that amount to 36 for the body of the scarf.