It can be done... IIRC, the drive will sit right on the internal metal shielding, and you just eliminate the stock drive caddy. I had the DCE internal SD/FF, IDE-Fix "Express" module, and IDE drive all inside the stock casing. (All those hacks gave my A1200 a real "ghetto-rig" feel, LOL.)
The shielding actually wont fit either. I mean, I was able to get it on there (after covering the bottom of the shield with electrical tape to prevent shorts) but it was bulging up and I'm afraid that might bend the circuit board over time.
I think I'll try getting a longer IDE cable and putting it off on the side somewhere.
The flash IDE is an idea, but I need to read more about how long those drives actually last. Sounds like theyve got a kinda short lifespan... hundreds of thousands of writes. Sounds like a lot, but if you think about it, its really not that much.