Fx impact air cylinder

Is there anyone out there that could build me a custom air cylinder for an fx impact? The reason I ask is sometimes when I am hunting with it and need to rest against a tree to take a shot, it can be slightly difficult to keep the gun level with the large CF bottle on it. I wouldn’t mind trying something longer and skinnier (I know I may lose some air capacity). It seems to me that it may offer easier shooting when using unconventional rests in the field. If anyone could point me in the right direction I would really appreciate it. Thanks guys!