i'd definitely be trying to get him down earlier, say around 7pm ish... at six months they can have 3-4 bottles per day (according to my type of formula anyway).... if i were you i would get the three bottles in, then let him wake for the fourth, and hopefully it is before you've gone to bed...

my girl is 7 months to give you an example of how we do her bottles:

between 6-7am bottle on waking, solids half an hour later
around 12noon, lunch (solids)
around 1.30pm bottle
around 4.30pm-5pm dinner (solids)
around 7pm bottle then bed, asleep by 8-8.30pm
in between feeds she may also have some toast or a biscuit if she seems hungry or i need a moment of peace.

up until recently i was giving her a fourth bottle at 10pm but then realised she didnt need it and could go through til morning... she does still wake during the night but just needs help to get back to sleep... she isn't actually waking for a feed.

HTH... you might find as he starts to eat more solids, the bottles will drop down, thats what happened for us.