Homebrew item that provides prepared spell

I'm trying to create an item (an amulet) which provides the wearer access to the Bless spell. It can be cast once per day without using a spell slot, and can also be cast using a spell slot as normal. I also want it to scale (so it appears under each spell level when Show Level-Scaled Spells is enabled). 

Currently I can add the spell without charges and it shows on the character sheet as "At Will" (and only under level 1 spells), or I can add 1 charge (min 1, max 1) and it shows as "1C" (but again only under level 1 spells). 

I thought I could maybe add it twice, once with the charges and once without, and just tell the player to mark off the spell slot manually when casting via the slot, but it looks like you can only add each spell once per item. 

Any suggestions on how I get the spell to show as a normal spell?