It's simple, actually.
526,LAPTOP,Laptop,Laptops,8,0,"A portable PC!",2,0,6,
Add that to the Item.txt PBS File and then find the following line in the scripts under the section PItem_ItemEffects:
ItemHandlers::UseInField.add(:EXPALLOFF,proc{|item|
$PokemonBag.pbChangeItem(:EXPALLOFF,:EXPALL)
Kernel.pbMessage(_INTL("The Exp Share was turned on."))
next 1
})
Hit the nice shiny enter key at the end of the last line and paste the following:
ItemHandlers::UseInField.add(:LAPTOP,proc{|item|
pbPokeCenterPC
next 1 # Continue
})
On a fresh copy of Essentials, it seems to be working perfectly for me.