Yes, unfortunately. I don't believe there are very many hackers around that are THAT hardcore. It would require disassembly of the HOST code, and probably emulation of the internal processor and memory structures of the radio itself.
You would have to either 1) use an in-circuit emulator that emulated the CPU in a real radio, or 2) find or write a emulator or runtime simulator that simulates the hardware environment of the radio. Then, you'd have to debug the HOST code, figure out where the bar-graph subroutines are (they are there for SmartZone trunking) and call them when in conventional mode. Then you'll have to patch or re-assemble the new HOST code, and write that to the radio's EEPROM.