<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by deant:
Depending on the airline, sign up for IDine. Spend a couple of bucks for lunch, charge it on your credit card and the miles appear in a few weeks. Cheap way to keep the account active.</font>
Of course, that works well for people who are either based in the US or have easy access to restaurants in the US. The poster asking the question does not appear to be in the US.
As others have already said, the answer depends on the airline, and is likely better asked in that airline's forum.
Mike