I'm sure there is a simpler way, in Houdidni you can just make it visible or replace geometry and I'm sure in XSI you can easily make it visible too but its monday and I'm not awake yet.
Perhaps you could modify Matt Linds Match Position script from the XSi tutorials and then modify it to also parent the object once matched to the bone then orient it to the bone:
ApplyCns "Orientation", selected, target
and make its size relative to the bone (grid used here for example):
dim lengthy
lengthy = GetValue(target&".bone.length")
SetValue selected&".grid.ulength", lengthy
SetValue selected&".grid.vlength", lengthy
I have script for bone replacement somehwere so I know this works but still being monday I can't damnwell find it, but modifyin Matts script with just a few added lines of code is fairly easy.
I thought I put the bone replacement scipt on XSInet but I guess not, I'll look for it. Sorry.