Two recent tweets from Stan Lee himself revealed that he will film his Thor cameo tomorrow.
smilinstanlee: Be assured, my brave Brigadiers, after shooting my Thor cameo tomorrow I’ll abandon my quest for stardom and lead you to glory once again
7 hours ago
and
smilinstanlee: For Asgard! I now retire to gird my loins ‘gainst the forces of evil and humorlessness! Till it be morrow, my noble ones—Excelsior!
7 hours ago
Personally, I would like to see Stan Lee as a Viking ^^