You would use what is known as a "Power of Attorney" - each state has a specific form. Call a real estate lawyer or a title company near where the property is located and they should be able to easily help you out. You might be able to find a form online also, but you will want to have a title company or lawyer review it before you assume it is valid and properly filled out.
The "easiest" way is to appoint someone (an adult) as your "Limited Power of Attorney" for the purpose of executing the closing documents for you - OR - you can try to see if facsimile signatures are acceptable and if yes, have the closing agent fax you the several documents during the closing - you sign and fax them right back (you both are essentially standing by fax machines for the process - OR - you might try the same thing if both the closing agent and your location have scanners - they send you a .pdf document, you print it, sign it and scan it and send it back electronically - OR - have your wife attend the regular closing - she signs everything she is supposed to sign - then the closing agent accepts all monies in escrow, the agent sends you all the documents by FedEx - you sign them and send them back and when they arrive back, the closing can be formally completed and the money and deed distributed/recorded. A Limited Power of Attorney is probably the simplest and easiest way for you to get this done. I can draft one for you if you want.