Almost every section of the GFDL has something prohibiting this.
2. Verbatim Copying
You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that...you add no
other conditions whatsoever to those of this License.
Which you plan to do in your proprietary work.
1. Applicability and Definitions
A "Modified Version" of the Document means any work containing the
Document or a portion of it
You may copy and distribute a Modified Version of the Document under
the conditions of sections 2 and 3 above, provided that you release
the Modified Version under precisely this License
Your database will likely be a work containing the Document or a part of it, so this section comes into play.
5. Combining Documents
You may combine the Document with other documents released under this
License under the terms defined in section 4 above for modified
Combination just refers back to sections 1 and 4, so it doesn't help you either.
6. Collections of Documents
You may make a collection consisting of the Document and other
documents released under this License...provided that you follow the rules
of this License for verbatim copying of each of the documents in all
And collection just refers you back to section 2.
7. Aggregation with Independent Works
A compilation of the Document or its derivatives with other separate
and independent documents or works, in or on a volume of a storage or
distribution medium, is called an "aggregate" if the copyright
resulting from the compilation is not used to limit the legal rights
of the compilation's users beyond what the individual works permit.
When the Document is included in an aggregate, this License does not
apply to the other works in the aggregate which are not themselves
derivative works of the Document.
You intend to include the GFDL data in a proprietary work that limits users' rights to the rest of the data contained therein, which this section does not permit. The implication of this section is that the license must apply to the other works if the collection cannot be defined as an "aggregate".
So I'm sorry to say that you'll have to do without that data unless you want to release your entire program under the GFDL. Unless you want to face section 9:
You may not copy, modify, sublicense, or distribute the Document
except as expressly provided under this License. Any attempt
otherwise to copy, modify, sublicense, or distribute it is void, and
will automatically terminate your rights under this License.