Is it possible to configure hard keys to function as call appearances?

Scenario: a 6867i is configured with 5 lines. But, so many buttons are in use for other purposes that there is only room for L1 and L2 line keys.

Goal: First call uses L1 button (regardless of which line it came in on), second call uses L2 button, (even if it arrived via line 3 or line 5).

Current behavior: Line 1 and line 2 use L1 and L2; lines 3-5 do not have a button.