ok, so this has either been talked to death, is programmatically impossible, or just plain far-fetched...
...but this is my concept of an IC2 implementation for adding personal inventory space.
Perfect for those extreme dungeon exploration expeditions, or for collecting the harvest from your 40x40 cane farms.
Sure, it's expensive to build. Good technology isn't cheap, you know!
The Compress-O-Belt(tm)
* Worn in place of Leg Armor.
*Provides 9x1 worth of additional inventory.
*Belt drains small amount of EU/t from backpack; internal capacitor allows for small interval of self-powered use to allow bat-packs to be recharged/swapped.
*Dropping belt, or belt running out of power causes belt to immediately empty items in extra slots, either into free inventory or onto the ground.
Possible recipes could include advanced components to take into account the arcane forces involved in matter compression of this type; ie
[chest]
Please forgive my vast void of knowledge when it comes to the technical side of Minecraft.
Thus, not knowing if this is firmly in the realms of wishful thinking, or actually plausible...