tricks for achieving high magnifications?

With the various correctors available now, getting low power in the binoviewer has become much easier. Sometimes, however, I find myself wanting higher powers than my setup allows. If you could achieve 4x or 5x easily with the binoviewer, this would allow planetary viewing with cheap and comfortable 20-30mm plossls. Has anyone found a way to do this using a barlow or powermate, before or after the diagonal, or some other interesting solution? My particular interest is getting more than the 2.5x my newtonian ocs + powerswitch allows when used in my refractor, so if anyone has any ideas, I'd be grateful.
thanks,
Nils

Here is link that may help.
http://www.buytelescopes.com/search.asp?q=TeleVue+Barlows&s=&x=18&y=7

Nils,
I believe that the refractor version of the Dual Arm Power X Switch offers 4x in the high power setting. The other powers are 1.4x, and 2.5x.

Ken....