To quote:
Epic Spell Levels: Epic spells have no fixed level. However, for purposes of Concentration checks, spell resistance, and other possible situations where spell level is important, epic spells are all treated as if they were 10th-level spells.
Emphasis mine.
As far as I'm concerned that would allow it.
This. Specifically, Uncanny Forethought looks at the level of the spell in question (10th, in this case), and then looks at what level spell slot you're expending. Since 10 = 10, it works.
Like CantripN said, it's definitely not what the designer's
intended, but that's never been a relevant assertion in CO discussions.
As to abuse, there's Miser with Magic + persisted
unfettered heroism (using the UA action point system) to refresh the slot 1/round all day long.