I use a compleletly different system for item creation, but instead of xp we use hit points, not permanent though.
During the creation process the character loses hit points representing the fatigue from building items. As players are doing this during adventuring it poses some significant risks.
Although we use a different system try 1 hit point per 10xp normally spent, and item creation as 1 day per 100gp cost.
As a option, a Wizard can elect to bond with the item. Bonding eliminates hit point drain during creation. Instead an eqaul number of hit points is placed into the item. If the Wizard is more than a mile from the item, he loses those hit points as long as he is separated from the item