Have you tried the PIC18F452 bootloader from www.microchipC.com? The
source is available for $50 (I believe).

--- In microchipC_pic18Fx_bootloader@yahoogroups.com, "jimdhlqst"
<jim@...> wrote:
>
> I liked the Tolmie bootloader for the 16F876, but now want an
> equivalent or better one for the 18F2520 (a nice upgrade for same
> footprint and functions and more i/o).
> Main features:
> -Only 3 wires to the device: RX,TX,G
> -Bootload and terminal auto share same serial port.
> -Boot begins with a code the device after reset. No timing issues
> -Simple small exe program remembers a compiled hex file and path.
>
> Wanted extras-
> C source for CCS compiler with a space for adding instructions such
> as i/o wanted set while booting.
>
> Maybe use hyperterminal. Slower, but I suspect that communication
> and computational time are quite small compared to actual flash write
> time.
>
> Another question: Can the differences in programming algorithm for
> the 18F processors be reduced to a simple table of block starting
> addresses(Or any kind of table)?
>