I'm not sure what you want to do here, but here are some thoughts anyway:
1. Amiga floppy can hold up to 880k not 720k / that's the pc capacity of dd 3.5 floppies. So, if you want to put something larger than 720k up to 880k on an amiga floppy you should be able to do it
2. If it's a pc you're transfering the files from to amiga, then, if it doesn't exceed the 720k size too much, you could try to unpack the lha on the pc and repack it with rar at best compression setting. It should produce a smaller file that might fit in a pc dd floppy and then unpack it with amiga version of unrar
3. You can always split and join files, check aminet, there's at least 1 splitter/joiner that works on pc+amiga.
Hope that helped a bit.
