This was unfortunately much more difficult than I had hoped. What I wanted to do was supply an absolute path for the asset upload, and have the paths for thumbnails built automatically by MovableType.
I was able to hack this into being by specifying the static directives as the asset url and path, like this:
First I tried this, but it wasn't what I wanted:* Edit /usr/share/perl5/MT/Asset.pm line 83:
: $1 eq 'r' ? MT->instance->static_path
Also line 62.
ACTUALLY NO - instead changed lines 1004 and 1009 in /usr/share/perl5/MT/CMS/Asset.pm
to %s instead of %r. This will move only the asset, not the thumbnail.
And MediaUrls helps for general media resources.