it's baby led weaning, so if he doesn't want it, that's fine, just keep putting stuff down on the highchair tray and get on with eating your own dinner (or do something else).
i personally wouldn't put things in his mouth... it's about letting them lead their own weaning and being in control, not feeding them up at this stage, so by removing control you are kind of defeating the point, iyswim?
i remember reading somewhere that you should get your DP to feed you an entire meal off a spoon one night to see how it feels and actually me and dh did try it for a laugh (not the whole meal, it was too irritating). it was a very interesting experiment, and convinced me not to put things in dd's mouth and let her take things at her own pace.
your baby may know something you don't... he may be going through a growth spurt and want more milk, he may have sore teeth, or he may just not be ready for weaning. if you look at the FAQ on the yahoo group you'll see that a lot of babies take a while to get the hang of it.
i have also found, by the way, that sometimes dd is happier munching on a ricecake in the buggy, or on a crust of bread in a cafe, than in her highchair. i guess it's because there's more to look at.