BackupMenu works correctly with multiboot (with multiboot patched) but it works at one condition.

The last booted OS before BackupMenu MUST BE MAEMO.

The ITEM script proposed doesn't suggest to multiboot a kernel to use, so multiboot uses the last flashed kernel.
If you will run BackupMenu after you have used Nitdroid or MeeGo, BackupMenu will not start correctly.

In these cases you must before boot to Maemo Os and then reboot to use BackupMenu
Or multiboot script must be changed to assure that BackupMenu will always be started with a Maemo's kernel (stock or power kernel)