Adding a "Class-Path:" entry to a MANIFEST.MF file seems to work for me.
The two entries were present in the command that was generated by the build
pack.

Ex:

`CALCULATED_MEMORY=$($PWD/.java-buildpack/open_jdk_jre/bin/java-buildpack-memory-calculator-2.0.1_RELEASE
-memorySizes=metaspace:64m..
-memoryWeights=heap:75,metaspace:10,native:10,stack:5
-memoryInitials=heap:100%,metaspace:100% -totMemory=$MEMORY_LIMIT) &&
JAVA_OPTS="-Djava.io.tmpdir=$TMPDIR
-XX:OnOutOfMemoryError=$PWD/.java-buildpack/open_jdk_jre/bin/killjava.sh
$CALCULATED_MEMORY" && SERVER_PORT=$PORT eval exec
$PWD/.java-buildpack/open_jdk_jre/bin/java $JAVA_OPTS -cp
$PWD/.:$PWD/.java-buildpack/spring_auto_reconfiguration/spring_auto_reconfiguration-1.10.0_RELEASE.jar
*:$PWD/another-new.jar:$PWD/some-new.jar*
org.springframework.boot.loader.JarLauncher`

This was with v3.4. If you're on an older version, you might try upgrading.

Do you see your entries listed in the start command that's generated by the
build pack?

Dan