Amongst other things:
1. Get an early start. If you can be on the road by 7.30, you will have got somewhere by noon. Then you can relax, hang out, eat, drink and people watch. If necessary you can get back on the road by 3 for another couple of hours. Seven and a half riding hours a day is enough on any tour!
2. Even though it's hot, you still need to eat, even though your appetite might be suppressed.
3. Some people do need mineral supplements when sweating a lot. I've used a small pinch of salt in a 50:50 dilution of Coke and water to good effect, and can be replenished anywhere.
4. Protect the back of you neck and head with a bandana or hat, but don't neglect the sunscreen on the shady areas either. Limestone chipping roads can reflect a lot of light back up at you.
5. Wash your shorts or liners every day. Consider getting changed at the three hour lunch spot and let the shorts dry out. If you can't wash them, leaving the pad exposed to the full sun during the midday stop will kill a lot of bugs. And fleas.
6. Monitor your piss. If the volume is less than normal or the colour anything darker than pale straw you need to up your water intake.
7. Monitor your mates. Know the difference between heat exhaustion (sweating, hot and dizzy) with heat stroke (dry skin, red hot, diminishing consciousness and imminent death). If in any doubt stop, get into some shade and drink.
8. Problems can accumulate. If you had a hard day and suffered a bit, be extra vigilant the next day. If you didn't get dehydrated at the end of the previous day you will already be in deficit when you start the next.
9. Don't be suckered by the difference between dry and humid heat. The body reacts the same way by sweating. The dry heat feels more comfortable because the sweat evaporates and you feel slightly cooler, but you are still loosing fluids at the same rate. However because you can appear not to be 'sweating', people often underestimate the amount they need to drink.
10. Don't run out of water. Try and plan ahead how much drink you will need between shops /cafes / fountains along your route (remember long shop closing times at lunch). If you think it's going to be more than one and a half to two hours, then you will need to carry more than just two regular bike bottles. Platypus do very light, screw top water containers that are also good around camp and allow you to take more water with you if needs be.
Don't underestimate the risks, but don't be too intimidated either. Start the trip slowly and build up. I love the heat.