This isn't really a tech-kern question, but never mind. You shouldn't need wedges at all, and I'd advise against trying to force them to work (it is probably possible, but far more work than you need to do).
Go back to your original kernel, and when that's running, do disklabel wd0 On NetBSD systems, when GPT isn't used, there is *always* an in-kernel disklabel. When there's a disklabel on the disc, the in kernel label is just a cached copy. When there's an MBR but no disklabel, the MBR is converted into disklabel format for the kernel to use (MBRs contain a subset of what a disklabel contains, including everything important). When there's no label of any kind, a suitable one will be synthesised. The output from that should show one of the partitions as an ext2 type partition. Then (assuming that happens to be partition 'e') just do mount -t ext2fs /dev/wd0e /mnt (adopted as needed to your requirements, add -r for a readonly mount, and of course, /mnt should be wherever you want it to appear). Unfortunately even though "since ext2 is supported by NBSD" is supposed to be true, I have come across (recent) ext2 filesystems that cannot be handled. kre