The problem is I need to do this at scale, quickly, in a whitehat way. I thought about pinging, hiring guys on Fiverr to submit to social networks or using Scrapebox's rapid indexer add-on - but I think that all of these solutions are going to look mighty suspicious to Google and result in penalties.
I would recommend not to use any of the mentioned techniques, instead try this
1) Upload a sitemap to Google Webmaster tools
2) Fetch as google in webmaster tools (website and some categories)
3) Create social profiles such as Twitter, Pinterest, Facebook and put your URL there. These sites have very high authority and get indexed all the time. Share the link in posts
4) Do cheap stumble upon discovery
5) Do cheap Reddit paid Discovery
6) Bookmark site in Delicious - just there
7) Write 10 blog posts, drive traffic to them through PPC, have a link back to categories or website
8) Submit RRS feed
9) Set up small PPC budget and get some clicks for very long tail and cheap keywords. Even if you get a lot of impressions and no clicks this is still visibility to google. So bid just enough to be on the first page and for the keywords that are cheap. Result - few clicks, a lot of impressions, and now Google knows about your site.
10) Monitor Webmaster tools and make sure that robots.txt is not blocking any URLs
I hope it helps