The direct answer to your question is no. What you are asking for is a stemming wildcard operator, and Google Search does not currently offer one. A stemming wildcard lets you identify a group of search keywords having a common stem (prefix). In other words, a stemming wildcard stands for part of a search term. The asterisk is not a stemming wildcard. It stands for a whole search term.

Interpreting your question more broadly, how could you get as close as possible to the search results you are looking for? There are two ways you could go.

Exact equivalent to site:csu*.edu, using stemming

It is possible to get exactly the Google search results that would be provided if the stemming operator was available. You must collect a list of domains and manually string them together with the OR operator:

keyword1 keyword2 [...] site:csu.edu OR site:csub.edu OR site:csubak.edu [...]

For EDU domains, use http://whois.educause.net/ to collect the list. At that site, enter the search csu%.edu (% is a stemming operator there).

This does exactly what the stemming operator would do. It would be useful, for example, to webmasters and others for whom nothing but a strict stemming of CSU will do.

You can copy and paste the resulting list into the Google search box, but you will still have to add the site: operator to each domain name, and the OR operator between each domain name. So one drawback of this approach is the tedious and error prone nature of the process.

Another drawback is that there is no guarantee that domains with the CSU stem are relevant. For example, csufresno.edu is a domain of Cal State, but csu.edu is a domain of Chicago State University, and csuniv.edu is a domain of Charleston Southern University. Furthermore, fullerton.edu is a Cal State domain, but would not be included in search results because it does not have the CSU stem.

Near equivalent to site:csu*.edu, using relevance

The other approach you can take is:

keyword1 keyword2 [...] "california state university" site:edu

This approach relies on Google to provide results within the EDU domain which are relevant to Cal State. It turns out that Google is actually very good at relevance. So, if you are not strictly interested in stemming but are more interested in relevance, that is the way to go.

For example, the search "student handbook" "california state university" site:edu returns results relevant to CSU student handbooks, even in CSU domains which do not have the CSU prefix, such as fullerton.edu.

Note

The site: operator adds an implied wildcard to the start of the domain that matches any number of keywords. This means that site:edu, site:.edu, and site:*.edu are equivalent. It also means that they will return not only results for csu.edu but also (for example) wcsu.csu.edu and origin.wcsu.csu.edu.

Perhaps this is because when linking to Google+ members the + is a prefix to the member name.

See, e.g, Google Kills Its Other Plus, and How to Bring It Back on Wired:

Google wouldn’t disclose exactly why they phased it out, though it seems obvious that they’re paving the way for Google+ profile searches. When Google+ launched, instead of adopting Twitter’s @reply syntax, they coined their own format for mentioning people — adding a plus to the beginning of a name — triggering the future conflict with the + operator.