Absolutely - put the system in Pool mode, put the lines into pool, the phones get 2 Pool 880 buttons, freeing up 2 buttons, 1 of which to use for DND.

Back up the system first, as when you go to pool mode, ALL phones except Ext. 10 will be pooled. You can then do a copy #399-10-11, 12, 13, 14, etc. skipping the extensions that should be pooled.

Make sure the customer is cool with using Intercom codes to pick up calls on hold, and parking at the pooled extensions for retrieval elsewhere.