Start, Run, type in this:
%CommonProgramFiles%\Research In Motion\Shared\Loader Files

Double click your OS directory (mine is 8100-v4.2.1.101_P2.3.0.80)
Double click Java

Keep these:
net_rim_theme_100_240x260_b.cod
net_rim_theme_bbdimension_zen_240x260_b.cod

Delete these:
net_rim_theme_102a_icon_240x260_b.cod
net_rim_theme_107_zen_240x260_b.cod
net_rim_theme_114_240x260_b.cod
net_rim_theme_115_240x260_b.cod
net_rim_theme_119_icon_240x260_b.cod
net_rim_theme_120_green_240x260_b.cod
net_rim_theme_120_today_240x260_b.cod
net_rim_theme_125_today_240x260_b.cod
net_rim_theme_125_zen_240x260_b.cod
net_rim_theme_bbdimension_icon_240x260_b.cod
net_rim_theme_bbdimension_today_240x260_b.cod

If you connect your Pearl and run desktop manager, then App Loader, and just click next, it'll delete the "unrecognized modules".

I'm going to update my script so it lets you delete themes per-carrier, but for now, the above should be easy enough.