I dont know what formation you are playing mate, but i had that problem with Chris Holroyd with Accrington. Then i played him as a lone striker with 2 CAM's and he started to score on a rather regular basis.
Last year especially Mangan scored a few for me when i had him at Eastbourne, but haven't looked at his stats on this one yet.
Hope it helps.
5 in 11 isn't bad mate. Some players score 2 or 3 in one game but then don't score for another 5 or 6 games but still end up with a healthy 20+ a season.
I signed Jack Tuyp last year and his figures read something like 40 games 4 goals in his first season at swansea. I kept faith with him and the following season he scored like 25 league goals.
Try getting a target man on loan from a championship/league one outfit. Might benefit him pal.
Striker, from Forest Green in BSP. Thought he was one of the best striker in BSP, but when your started a new game he on the ban until december.
Try set his role as poacher, but you will need player to back him up.
I usually use 4-4-2, that the other striker set as 'target man' or 'deep lying forward' and the mentality is support. That create many goal for the poacher. <)