Add Goal to VisitorID

I want to add a Goal to a VisitorID manual.

This why:
Visitor visits the site and clicking on a extern affiliate link with the visitorID. Exmaple (伸縮大容量環保購物袋 [] - NT$1,099.00 : Onlineshoptw Online Store).
After 24 hours its possible to check if the vistor bought something. If this happend the Subid (also VisitorID ) has now a sale and reached a goal.
Now i want to set up a cronjob that add to all visitorids which bougth something a goal. Like piwik.php?siteid=1&visitorids=1234&goaID=1

Is this possiable or have your other ideas for external reaching goals (its not possible to add own javascript on the external site)?

i found a solution with the php api

$t->setVisitorId( “33c31e01394bdc63″ );