TM4C123GH6PM: TivaC flash bootloader load address

I have successfully built the TivaWare flash-based serial bootloader (boot_serial) and loaded/run a test app using LMFlash utility.  The bootloader is in flash at 0x00000000 and the test app is at 0x00002800 following the recommendations to modify bl_config.h and the linker control files for boot_serial and the test app.   

I am tasked with using the flash-based bootloader to do app-initiated updates of the firmware app located at load address 0x00000000.   This is an app built in the Energia where the load address is fixed at 0x00000000.  So I am attempting to change the TivaWare flash bootloader address to 0x00002800 by modifying the boot_serial linker control file to read:

MEMORY
{
    FLASH (RX) : origin = 0x00002800, length = 0x00010000 - 0x00002800
    SRAM (RWX) : origin = 0x20000000, length = 0x00010000
}

However, when I attempt to load the app, LMFlash cannot communicate with the flash bootloader:

I am aware from spmu301e.pdf that the bootloader is located at 0x00000000 and that APP_BASE specifies the app location, but is it possible to change the bootloader location?  Ultimately I will be invoking the bootloader for app update from the app itself.   Any help is appreciated.