Ah okay so more than a read only link, I understand.
Yeah that is not available at the moment.
Many split work up into teams + projects or portfolios.
You could also have main tasks assigned to you and subtasks to the client but yes that also means these subtasks have to be multi-homed into another project unless they only view them under their my tasks.
I mean the multi-homing can easily be automated by rules and would not create more manual work for you.
Some more great ideas / options of working with external clients are listed here.