Interestingly, the only place I'm aware of stacking temp hit points being addressed is the 3E Main FAQ, which gives a bizarre answer:
How is the body feeder weapon quality supposed to work?
Do the temporary hit points from the weapon stack? The
same question applies to mind feeder weapons and to spell
effects, such as vampiric touch.
Temporary hit points from a body feeder weapon stack with
each other, but not with temporary hit points from any other
source. Likewise, temporary psionic points from a mind feeder
weapon stack, but not with temporary psionic points from any
other source.
In general, any effect that allows you to gain temporary hit
points over time allows you to stack those points, but only
those points. For example, if you use the vampiric touch spell,
the temporary hit points you gain from that particular casting of
the spell stack. They don’t stack with the temporary hit points
you get from an aid spell, nor would the effects of two
vampiric touch or aid spells stack. If you were to use two body
feeder weapons (or two mind feeder weapons), you could not
stack the temporary points from the two weapons.
According to this answer, then, two False Lifes would not stack (like two Aid spells), nor would False Life and Heroes' Feast (like Vampiric Touch and Aid). Arguably, a Repeated False Life spell (theoretically describable as an effect that allows you to gain temporary hit points over time) would stack with itself when it repeated.
Now, whether one considers this answer meaningful or useful is another question.
-Hyp.
