Faking RWTS13: Trying to figure out how to do something

[Lyrical Nanoha <LyricalNanoha@dosius.net>]

I'm trying to write a clone of Boot13, and unfortunately a method I 
planned to use which works fine with a 16-sector ROM doesn't work with a 
13-sector ROM.  Apparently the 13-sector ROM has some sort of 
jump-back-to-self or weirdness that simply relocating isn't going to help. 
So I figure maybe the trick is to strip down RWTS13 to what I want.

I have a disassembly of RWTS from DOS 3.2.1, but I can't quite get my 
hands around it.  All I want to do is something like this:

        lda     #$60
        sta     slotno
        jsr     rdboot
        bcs     error
        jmp     $0301
error:                          ; couldn't load boot sector

or something like that.  (It looks like the boot sector is loaded at 
$0300, so we might have to be careful.)

-uso.