UMD: Emulate a Class Feature

[Yogibear41]

In another thread I posted, a suggestion was made to use UMD via the Emulate a Class feature rule to emulate the ability to cast spells in order to power a runestaff.

I was curious if anyone has done this before or whether it is even something you can do. If you could make the neccessary UMD check could you essentially use the staff at will?

[Troacctid]

Use Magic Device explicitly allows you to sacrifice daily uses of abilities you don't have, but I don't see anything that would allow you to break the Runestaff's daily limits.

[Yogibear41]

Use Magic Device explicitly allows you to sacrifice daily uses of abilities you don't have, but I don't see anything that would allow you to break the Runestaff's daily limits.

Oh I was reading about runestaffs in the wrong spot, I didn't see they were each 3/day.

[Troacctid]

The other concern, of course, is that if you're activating something like a shield of vigor by emulating the Knight's Challenge feature of the knight, well, say you manage to emulate a 2nd level knight, that means your effective knight level gives you 1 + Cha uses per day of Knight's Challenge. IMO you'd still be beholden to the daily limit you would have if you were a knight of that level, so after you've used it that many times, the DC of the check would basically increase accordingly.

[Crake]

Use Magic Device explicitly allows you to sacrifice daily uses of abilities you don't have, but I don't see anything that would allow you to break the Runestaff's daily limits.

I have yet to encounter a DM who allows you to expend a resource you don't have, despite the example in the PHB (which is decidedly absent on the SRD), so take this recommendation with a massive grain of salt. I personally allow casters to use runestaves (and knowstones from one of the dragon magazines) to cast spells not on their spell list with a UMD check, but they still need to actually expend their own spellslots to do so.