Is there any way to be eligible for grants before getting 501(c)3) status?

Summary:

Sometimes, a fiscal sponsor will assume responsibility for a grant-supported project that is not connected to any existing agency or organization.

From the BOARD CAFE for June 2000:
If you're a new organization that hasn't incorporated yet, but
wants to start activities and accepting tax-deductible donations,
you may want to use a fiscal agent or fiscal sponsor. And if
you're an established organization, you may want to help new
community efforts by serving as their fiscal sponsor. A set of
Frequently Asked Questions (and answers!) on the legal and
contractual responsibilities for fiscal sponsorship partners is
now available on the web at the Nonprofit Genie: go to
http://www.genie.org and select "Fiscal Sponsorship" in the
"FAQs" section.

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There is more information about fiscal agent arrangements in the general
FAQ article on starting a nonprofit organization at
http://www.nonprofits.org/npofaq/2/1.html