our dog sleeps inside. we got her as a young pup so went through the toilet training thang...outside on a lead after dinner (hers) and just before bed time and would go on repeat 'do a wee' and when we saw her squat down to wee/poo we would say: 'do wee/do poos'. that way she learnt the association. we also had a section of the kitchen area (which was gated off from the rest of house) that had newspapers down in case of 'accidents'.
it took a bit of time, but she got there and now can wait aaagggess before needing to be let out for a wee in the morning.

i guess with the dog only being new to your house it will take some time, and being *slightly* older it may take a bit more for him to twig what the deal is. in your situation i would cut down on the night wees to just the one after dinner, and then again at bedtime. use heaps of positive reinforcement when he wees outside and then back in. create a little area for accidents...they tend to understand it pretty well, give or take of course, and then wake up quite early and let him out for a wee in the morning. eventually you will find that he builds up his ability to 'hold on' as he has the structure and routine to go by.

hth!