You are talking about that voltage drop at idle right?
IMO, your best bet would be to either to not worry about it - not the best course of action since it's hard on the battery, but XS power carries a 3 year warranty. I've found that the brake lights on this car draw gobs of power and using the e-brake to hold you at stop lights helps quite a bit
Or bite the bullet and get a high output alt (make sure you ask for the 14v regulator and not the 14.8v regulator that comes on most of them standard)
DC, Mechman, and Singer are all top tier products. Excessive amperage is midrange. Anything else such as powerbastards or other ebay brands I would never touch
I also seem to recall reading on here that an alternator from a legacy? Outback? Something like that will swap right in and has a higher amperage rating than stock. Not sure about idle output though
Final option would be to swap a smaller idler pulley on there. I'm not familiar with sizing for this. However, if you call up DC power they may be able to help you. Ask for either Anthony or Kyle. They might be able to tool you up something. This would help your idle output and alternator cooling since it's spinning faster. But the tradeoff is that it spins faster... Expect lesser bearing and brush life