I use "be clean" for a wee and "do you business" for no. 2
But wee and poo are fine as long as he knows what it means.
I would work on the instilling the "cue" word - although as they dont go so much at 7 months as they do as 8 weeks so it will take longer. Every time you catch him doing it, say the cue word then praise. Unfortunately its not the perfect time of the year to spend ages in the garden waiting for him to go - but I would probably take him for the 30 minutes then stand in the garden.
YOu could also work out how long he can go between "wees" and then try and take him out when you think he should need to go.
I take it he usually does it overnight - if so, try restricting the space he has so he only has room for his bedding (they dont like to soil their bedding).