Originally this response read:
No, it's not possible with BIND.
In most cases I wouldn't think it would be particularly
useful, either, but that's up to you (and perhaps you
regularly deal with some domain that has very poorly set
TTLs. If you absolutely must, there is an option in BIND
that will allow you to set a minimum floor for TTLs.
I am still skeptical concerning whether it is necessary in the general case, but there has been demand for this feature and as of BIND 9.10, ISC is introducing a new prefetch option -- below is the release note entry for this feature from the current 9.10 development release (presently 9.10.0b1):
The new "prefetch" option can improve recursive resolver
performance: when it is in use, cache records that are still
being requested by clients will automatically be refreshed
from the authoritative server before they expire, reducing or
eliminating the time window in which no answer is available
in the cache. [RT #35041]