Given the recent e250R i2c rom dump, MrH brought an analysis of what the rom actually contains and it is indeed the pre-bootloader code that loads the bootloader from the NAND flash and starts it. The perhaps most interesting part is that the e250R’s i2c rom dump is identical to the vanilla e280 one we have… meaning that they both load the bootloader the same way!

So here’s MrH’s suggested steps (keyed in on the wiki page by me) to convert your R model Sansa to make it capable of loading and starting the Rockbox bootloader.