Hi XT, you are right in that AIM has no influence on what the US tax code considers short term or long term gains.
Because I am expecting to stay with this for many years, and I know the LT gains are taxed at 20% versus ST gains being taxed in the 30%+ area, I want to use the method that gives me the most LT gains I can get over the life of the AIM account.
This all gets dealt with on Schedule D on the tax return, and Uncle Sam will not complain if you simply report everything as ST gains -- but you may pay more tax than is necessary.