Let the user choose the keyword for my omnibox chrome extension

I just created a chrome extension using the omnibox api.

"omnibox": { "keyword" : "a" },

I found out that it is not possible to use multible keywords or let the user choose a keyword for my extension although the extension is listed on the search engines settings page:

I addition to that the priority of the extension keyword is by far the lowest. If a User already defined a keyword in the Default search engines / Other search engines - sections the extension keyword is not usable.

Does anyone know a solution for at least one of these issues?

Maybe by using the NPAPI?

I'd like to let people know that it appears that this has changed and is no longer the case. I was exploring this possibility myself and found this page stating it wasn't possible. In order to change the keyword for my extension after installation I took the following steps:

1. Right click the omnibox (address bar) and select Edit Search Engines
2. Scroll to the very bottom (optionally deleting half of the really long list of sites you'll find)
3. Under the section for keywords for installed extensions, find the extension you wish to edit and click the keyword value to the right of it's name. There is no edit button, it will turn into an editable field.

I am using Chrome version 30.0.1588.0 on Windows, but I am not sure how long this has been editable.