ARMASM - leaving an empty gap at fixed memory addr

I am writing a C program that will be loaded into flash memory while the target device is already running; in other words, this C program is NOT run immediately out of reset.

I need to modify the startup.s file to provide the following layout when linked with my C code:

Start of module:
ValFlag, a 4-byte validity flag at start of the module,
Branch instruction to module execution address,
Header, a 256-byte empty area of memory (starts at ValFlag+0x10),
Execution address and remainder of code.

I'm having problems generating the Header area. I can't figure out how to force the assembler/linker to leave a gap at exactly that address range. The linker must not generate ANY hex records for this area of memory. This area will be overwritten later with custom hex records containing info such as CRC, copyright, etc.

I suspect this is normally done with the scatter file, but I really want to avoid that. I would prefer having the IDE generate the scatter file from the target options settings, to minimize the chance for errors should someone need to move this module to another area in the target device's memory.

Karl