I had earlier written about a custom google search engine that I had created that helped me look through my delicious bookmarks. The search engine was great, just that I did not have other features that Google was offering, things like definations, books, etc. It looks like the Google default search cannot be done away with, thats the reason I wrote this small greasemonkey script that shows the results from my search engine side by side of Google results.
The script itself is simple, it gets the search parameter and pages from the location, sets them in the Google CSE Url and makes an AJAX call. The results are put into a div thats placed next to the results div. All decorations except the search results itself are removed. That done, the sponsored results table is also blanked out to use that space for custom search results.
If you want to add your custom search engine, simply reaplce the first variable in the page with your value - this is the cx parameter passed when you search on your custom search engine.
While I am at it, I was also planning to convert this to a ubiquity extension.