How to deal with heat/humidity?

To all you 'tropical runners': I live/run in Bangkok, and my performance falls off a cliff come Feb/March when it starts getting really hot. Last night's 10k was at 7:30, 33C and 70% humidity, and felt like 15k. I've been running here for 20 years, (5-10k, on and off) but serious about running for the past 2+ years, and noticed the same pattern last year: lame and slow in the heat and springy and fresh for 8 weeks in the cool season. Is there a workaround so I can push harder and get faster even in the heat? (I guess being 55 doesn't help much, either) Suggestions highly appreciated!