No, spells don't stack with themselves, so heroics can't be used twice, or used to qualify for other feats.
Spells that provide bonuses or penalties on attack rolls, damage
rolls, saving throws, and other attributes usually do not stack with
Same Effect with Differing Results: The same spell can sometimes
produce varying effects if applied to the same recipient more than
once. For example, a series of polymorph spells might turn a creature
into a mouse, a lion, and then a snail. In this case, the last spell
in the series trumps the others. None of the previous spells are
actually removed or dispelled, but their effects become irrelevant
while the final spell in the series lasts (PH p171)
A feat granted by the spell does not count as a prerequisite for another casting, since a second casting removes it, and if you lose the prerequisite feats you cannot benefit from them for new feats.
A character cannot use a feat if he or she has lost the prerequisite. For example, if your characters strength drops below 13 because of a ray of enfeeblement spell, he or she can't use the Power Attack feat until the prerequisite is met again (PH p87)
Mouseferatu one of the designers says that it does not work to build up to greater feats.
"For the duration of the heroics spell, the subject can use the feat
as if it were one of those the creature had selected. All
prerequisites for the feat must be met by the target of this spell."
If I may put on my Hypersmurf disguise for a moment...
It says the subject can use the feat as if he selected it, not that he
is treated as having selected it. And since the target must meet the
prereqs, a feat granted by the spell does not qualify.
And is flexible on whether it should apply, reading it both ways.
Though it could be better worded, I believe that clause doesn't apply
here. The example given is polymorph, and the intent seems to be "same
effect with differing results that cannot all exist at once.
After all, if your interpretation is correct, it means that nobody can
ever benefit from, say, resist energy (cold) and resist energy (acid)
at the same time. And while that's certainly a viable reading of the
letter of the rules, it's not the only one--and I don't believe it was
OTOH, given that I've long had a problem with just how many things
stack, and how long it can take a high-level party to prep for a
single combat, maybe I should give the more restrictive interpretation
So, based on that additional source, it's probably up DM discretion whether you can use more than one, but they don't act as prerequisites. He sees it as a balance issue, and a time issue, though, to allow multiple castings.