If you MUST do such a thing, then lirpa79 gave you a good suggestion.
However, I shall point out that it is EXTREMELY RUDE to mention gifts on the invitation (wrapped or otherwise). An invitation should NEVER state what type of gifts are requested, where the honoree is registered, what dollar amount to spend or anything else of that nature.
I repeat, NEVER should any of that information be included on an invitation (or on an insert card); it is rude, tacky and ill-mannered to do so.
GIFTS are just that - gifts. Guests are NOT obliged to give a gift in order to attend a party (otherwise, said gift is nothing but an admission fee).
Furthermore, guests who CHOOSE to bring gifts are allowed to bring them in any manner or format in which they choose - wrapped, boxed, bagged, unwrapped, shrink wrapped, etcetera.
The ONLY say the recipient has in the matter is the words, 'Thank You,' which should be said to every person who brings a gift (and then followed by brief written notes of thanks mailed to each guest).
Period.