Vendome 41's got his mounted on the front underside of his 1100's beak. There are a couple of bolts you can use for this.
I paid the extra money to avoid the hassle and got a set of City Slickers, they mount in place of the standard horn!
On the BOS they mount on front crash bar mounts, one either side.
Try to get an anti vibe mounting in some way (for airheads anyway) I've lost two due to fracture of the steel strips on the GS, nylon seems to work if you have acces to some (but then you need to connect an earth for them to work obviously)