It's not possible, sorry. If you wanted GBA compatibility you should have gotten a slot-2 device. There is no emulator, and it's unlikely that there will be a usable one in the future due to the way the GBA works.
However, I believe if you have a DS Lite you can try the EZ-V expansion pack. I think (not entirely sure though) that some people have managed to get it writeable from within an M3 Simply. I would do some research on it beforehand though.
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