Back in the late 60's an azalea hedge was planted in the side yard of our property. A number of the original plantings on the right side have since died, and there is now a mature maple directly behind the hedge (and with its roots growing into it) that wasn't there when the hedge was planted. I'm looking for suggestions to fill in the gap with minimal disturbance of the tree.

Existing plants in the hedge (left to right): Japanese spindle,
white rhododendron & formosa azalea behind a row of mixed dwarf azalea and yellow iris; 2 'autumn sunset' azaleas; 2nd grouping with another white rhododendron, a crepe myrtle that won't bloom & more iris