Rules requiring source+binary uploads to debian-backports?

Potentally stupid question.  I want to upload the latest version of
efsprogs from testing to debian-backports.  In that version, there is
a "new" transitional package, fuseext2.  It's not "new" in that
fuseext2 use to be built from a difference source package,
src:fuse-umfuse-ext2 which has been abandoned by its upstream, so
we've replaced fusext2 with a shell script which emlates its CLI in
terms of e2fsprogs fuse2fs.

However, it is "new" in that

(a) it's new to the e2fsprogs source package.

(b) it's new to debian/backports since there has never been a backport
of src:fuse-umfuse-ext2.

So.... do I need to do a source+binary upload, or will be OK to do a
source-only upload?  (All of the other binary packages are in
debian-backports since e2fsprogs has been previously uploaded to
debian-backports.)

There are no instructions that I can find on point in
https://backports.debian.org/Contribute, and the text in
https://wiki.debian.org/SourceOnlyUpload don't go into enough detail.

Also, if I have to do a source+binary upload, the comments in
SourceOnlyUpload entry in the Debian Wiki about the package not being
eligible to be transitioned from unstable to testing aren't really
applicable for debian-backports, right?  So do we have any enforcement
of the desire that source-only packages are considered desirable for
the Debian archive when it is for debian-backports?

Thanks,

					- Ted