Then my point of view is:
The flash only contents the RAM_downloader and a little interface to start the program.
1st. Download at the flash the new downloader.

This new_downloader must do something like:
Wait for the input of the 'real' aplication
Control the execution of the student's soft.
The download can be done from .bin (it is easyest)

If you use some interrupts for the new_downloader put a conditional jump at the start of the routine for jumping to the ram if the 'real' app is working.

2nd download the 'real' app
After this execute the new code. Change the condition for redirecting the interrupts to the external ram


Example
ramstart equ 1000h
org 0
ljmp start
org irq1
ljmp code1 ;first used irq
org irq2
ljmp code2 ;second used irq
org irq3
ljmp redirected_irq3 ;Not used irq
start: ;your downloader code
...
...


code1: jnb conditon,lb1
ljmp redirected_irq1
lb1: ;The new_downloader irq1 code
...
...
reti

code2: jnb condition,lb2
ljmp redirected_irq2
lb2: ;Teh new_downloader irq2 code
...
...
reti

; The user's code will be:
org ramstart
redirected_reset: ljmp new_start
org ramstart+irq1
redirected_irq1: ljmp xxx
org ramstart+irq2
redirected_irq2: ljmp xxxx
org ramstart+irq3
redirected_irq3: ljmp xxxxx

If you want to start from 0h you can download to RAM the program, cut the power, change EA and power on again. It was discussed the posibilliti of changing EA while power is on but i dont remember the result of this discussion.

Good Luck