you can't. Google does it on purpose when it thinks that the other pages are too similar to ones that it has already shown.
How do I write a query that will AUTOMATICALLY bring up all results for the subdomain without me having to click on "...show omitted results".
Take the following example:
hostname:www.imeche.org.uk inurl:events_research modern
Now, what this does initially is bring up the homepage for my site
where the keyword "modern" can be found.
I initially thought that the query above would only return results for the start page of the subdomain (in this case events_research/index.asp), as this is the only page that is displayed initially.
However, I noticed that you can expand results in Yahoo! (as in Google):