This is already the best way for a flat distribution(*). However, this doesn't mean that the internal pages have as much PR as the home page.
A rough calculation yields the following relation: PR_home / PR_internal approx (N-1)*(1-d)/d, where N is the number of pages (N >> 1) and d is the damping factor. PR is the real PR and it was assumed that PR >> 1.
If you want to distribute PR more equally, I would get external links to different internal pages. However, as long as the number and quality of incoming links (and the number of pages on your site) doesn't change, a total flat distribution would lead to a PR4 for all pages (at least in your case). However, the PR for the internal pages would be increased (even if they would be still a PR4).
(*) Of course, there are linking structures which would lead to a more flat distribution. For example, you could remove all links to the home page from your internal pages. However, this doesn't seem to be a pratical solution.