It is more important that the temperature of the eggs stay constant than it is to keep them a 88-99 deg. You can incubate as low as 85 it just takes longer. Just be sure wherever you put them the temp is constant and humidity stays at or above 90.
If you do not already have an incubator you can make one quickly and inexpensively with an ice chest, tupperware, vermiculite and a fish tank heater. If you need instructions let me know and I will post them.