While there really is no way to tactfully ask for money in lieu of wedding gifts, if you do not register anywhere, most of your friends and family will take the hint. Since most of your guests will be people you and your fiancée are acquainted with, they will know that either you have everything you need to set up your new home together, or that you are the type of person who enjoys shopping for yourself. Some people may ask a close friend or relative about what things are needed, and then it would be appropriate for the answer to be that the couple has everything under control. Again, most people will take the cue and send a monetary gift. Under NO circumstances should your wedding invitation state anything regarding gifts and/or money! This is considered very tacky and bordering on rude.
You might end up with some unwanted gifts, but most department stores will gladly give an in-store credit or even refund the purchase price, even without a gift receipt. When you write thank you notes, express your gratitude for the item you received. You do not need to mention you returned it. There is no need to have hurt feelings.
Some couples that have all they need of day-to-day items might decide to register for only formal china, crystal and silverware. No matter what you register for, the gift registry information should never be included on your wedding invitations. This information belongs on the shower invitations, or on your wedding web site if you have one. A good thing to keep in mind when it comes to questions like this is to ask yourself how you would feel if you received an invitation that requested money or only high-priced gifts. No matter what type of wedding gifts you receive, always remember to be gracious in your thanks.