My sister ran into a similar scenario for her wedding. Except in her case, she wanted to have an extra bridesmaid. In the end, there was an uneven number of wedding attendants (4 bridesmaids and 3 groomsmen), but what she did was have both my other sister and I (who were bridesmaids), be escorded down the aisle by our brother (who was one of the groomsmen). In all of the wedding pictures with the bridal party, the three of us siblings were grouped together. She had a great photographer who chose poses for photos that didn't accentuate the unevenness. I'm not sure if this helps or not...just wanted to give you another option, if you wanted to have him as a groomsman.