You may be able to use a solution that I found when
I had a related problem with installing 3.4 to hd.

(I found an incompatibility between the recent ext2
version chosen by knx hdinstall, and some other
less-recent ext2-handling software which I wanted
to use in connection with this partition.)

(1) set up your own chosen ext2 partition/fs in advance
of using the hd install script.

(2) modify the install script so that it doesn't make
a new filesystem on your chosen partition any more
and/or doesn't abort any more when you refuse to
allow it to format your chosen partition with a new
filesystem.

(3) run the modified install script.

I hope that helps.

Terry