Here is a simple diminished chord substitution that I now use sometimes over dominant chords. Here is a example of the first two chords of Sweet Georgia Brown and each one is followed by 2 diminished chords which can be used as substitutions. The first chord is E7 and the second is A7. Note the difference in the position of the substitution. Over the E7 I use the tri-tone and over the A7 I use the arp starting with the major 3rd. I am also showing here that each diminished chord is movable by a 3 fret increment.
——–|——–|-
—9-6–|—5-8–|-
-7-7-4–|-6-3-6–|-
-6-9-6–|-5-5-8–|-
—8-5–|—4-7–|-
-7——|-5——|-
Practice playing along with the song and try experimenting with the substitutions. If your lead player is trying to play diminished runs over dominant chords you might help him out by using this kind of sub.