txtsetup.oem and upperfilter

I have written some PV drivers for accelerating Windows under Xen. Some
of the drivers involved are:

Xenpci:
This is a bus driver that talks to the xen ‘backend’ and enumerates
child devices (network, block, and scsi-passthrough).

Xenconfig:
This is an upperfilter for each child device that creates a page of
memory and adds it to the resources in the START_DEVICE IRP. Before
passing it down, it also pre-populates the page with some configuration
‘commands’ that xenpci interprets, and are then available to the child
device. These commands come from the registry, and constitute some stuff
that has to be done at PASSIVE_LEVEL and hence can’t (shouldn’t) be done
in the scsiport driver (certainly not at HIGH_LEVEL when a crash dump
occurs anyway)

Xenscsi:
This is the driver for scsi passthrough

I need the above 3 drivers loaded at textmode setup time so that I can
use them for doing test-restores with Backup Exec’s IDR. I can’t seem to
figure out how to attach the upper filter in the txtsetup.oem… any
suggestions? Obviously the upperfilter is done in the inf file but I’ve
been lead to believe that a lot (all?) of the inf file is ignored at
textmode setup time, so it has to be done via txtsetup.oem.

A previous version of xenscsi didn’t require the xenconfig stuff and
worked fine in txtsetup.oem, but I’ve moved on since then and it would
be a pain to have to go back again…

Thanks

James