Turns out it's pretty easy.
Just replace the lbPrevLink and lbNextLink codes with the contents of the :hover and delete the :hover psuedo class.
#lbPrevLink {
left: 0;
background: transparent url(./slimbox/prevlabel.gif) no-repeat 0 15%;
}
#lbNextLink {
right: 0;
background: transparent url(./slimbox/nextlabel.gif) no-repeat 100% 15%;
}