what to do if subject header isn't encoded?

Hi,

I've met difficulty when I've tried to convert one maillist 
archive.

I use the following (was got from mhoarch manual) settings in 
rcfile

<CharsetConverters override>
plain;          mhonarc::htmlize
default;        MHonArc::UTF8::str2sgml;     MHonArc/UTF8.pm
</CharsetConverters>

<TextClipFunc>
MHonArc::UTF8::clip; MHonArc/UTF8.pm
</TextClipFunc>

The problem:
For example, if subject header is not encoded such as
Subject: =?koi8-r?B?UmU6IPPr8u/s6e7n?=
But looks like
Subject: Raw koi8-r cyrillic text

Mhonarc couldn't detemine encoding of the field and ruin it.

Question: Is it possible to specify that if subject isn't encoded 
mhonarc should think that the header is in KOI8-R?

Thanks.