As a temporary workaround, creating a symlink named dbclient pointing to dropbearmulti and executing scp with '-S' option explicitely specifying the path of dbclient symlink could work:
tc@box:/tmp/testdb$ mkdir -p mnt/dropbear
tc@box:/tmp/testdb$ sudo mount dropbear.scm mnt/dropbear/
tc@box:/tmp/testdb$ ln -s mnt/dropbear/localbin/dropbearmulti ./dbclient
tc@box:/tmp/testdb$ ./mnt/dropbear/bin/scp -v -S /tmp/testdb/dbclient dropbear.scm user@shell.org:
Executing: program /tmp/testdb/dbclient host shell.cjb.net, user user, command scp -v -t .
WARNING: Ignoring unknown argument '-v'
user@shell.org's password:
Sending file modes: C0644 118784 dropbear.scm
Sink: C0644 118784 dropbear.scm
tc@box:/tmp/testdb$
tc@box:~$ ssh -i .ssh/dropbear_id_rsa user@shell.org ls -l drop*
-rw-r--r-- 1 user users 118784 Apr 4 08:49 dropbear.scm