well …i do believe that the Vajazzle is going to be part of his birthday present….remember you promised us an update!….apart from that you could arrange for you to have just time for the two of you by arranging babysitting & restaurant booking or some other activity or you could do homemade vouchers for things he likes.
A great suggestions – buy 40 small /funny / cheap presents from the children.. we did this last year..
like
Nail clippers / choclate bars / lotto ticket / comb / mug/etc