I know you want to hear good news by the tone of your post. But there is a whole lot of challenges. You could put 650b wheels on and wider tyres might drop your bike down a little bit. The problem is you then have to worry about the top tube length. Can you still reach the handlebars easily? I don't know its your body. Reading thing like this when you're not in the bet of moods yourself makes it really difficult to say, but its a bag full of compromises. If you wanted to you could make the person suit the frame but its better off to start with a frame that suits the person.
On the plus side, so long as you can physically stand over the frame where a flat top tube would be you can still ride the bike without any problems.
Last edited by 1500SLR; 04-12-18 at 03:47 AM.