Would it be possible to add a General (Generic) Category? There are sometimes questions that do not necesarily fall into one of the Solution Categories.
Or create another section seperate from the 'Solutions' categories that could include; General, Education, Ariba user required Job Postings, etc.
By creating a user forum, that expands on the possible content, you may be able to drive more utilization and interaction.
Not sure if that is in the vision, but I know it has ben successful on other software platform grassroots User Forums.