Ok, promoted the 2.308 to extras testing, please test and vote:
http://maemo.org/packages/package_in...c-theme/2.308/

Also updated the opening post's instructions about coverting themes into schemes:

CONVERTING OTHER THEMES INTO PLASTIC SCHEMES - version 2.308 or later only!
You need to have package called "rootsh" installed, so install that first from extras. After that you just need to copy the desired theme folder into /opt/plastic-schemes/ folder and that's it.

Detailed instructions:
- First we need to find out the folder of the theme to be converted. Type these into xterm:
That will give you list of installed themes (their folder names actually). Built in themes are stored in folders "alpha" and "beta". Alpha = NSeries, Beta = Digital Life.
Don't care about folders called "Raleigh", "Emacs" or "Default", they are not actual Themes.
If we want to make Digital Life to be Plastic Scheme, then we would use this command:
Note that we will name the target directory as "DigitalLife", that's the text shown @ Plastic Theme Setup as scheme name. That cannot contain whitespaces, but capitals are allowed.
You can replace the "beta" with the theme directory you want and also the "DigitalLife" with name you want.

If we want to convert the NSeries theme to Plastic Scheme, then we would use this command:
You must be "sudo gainroot"ed all the time or copying will fail.