At least Cathay Pacific allows this using Asia Miles. Try this link.

http://www.asiamiles.com/am/1,,83099_84947_eng,00.html

However I've found that a call in advance to the airline (perhaps mention you're moving countries if applicable) will normally secure extra allowance of 10 to 15kg. Just ask for the approving managers name or reference number. Singapore Airlines and Cathay both did this for me a number of times with no problem.