The "easy" way is to use a 3.z ROM.
The "difficult" way is to cook your own ROM with a different set of devices.
The "middle" way is to add a line or 2 to your startup-sequence to use an upgraded .device or .library. Big ass thread on it here, Thomas Richter was very patient with noob me on this...
http://www.amiga.org/forums/showthre...t=Loadresident
The "middle" way means your boot disk still has to be under 2Gb and use Fast File System, but at least other partitions can be bigger.