any slice can be set as the default input slice by selecting it in the main playback page. but then you still have to lock all the others.

you could try programming your pattern in groups of 2 slices. Lock your main one and copy it to the buffer. Now choose another slice as your default using the playback page. You can now program the pattern with a combo of the default slice and the one copied to the buffer (by pasting it in as required) to get the meat of the groove down.

other than that it’s live entering or locking.