I'm not sure that this will help :
I have created my own chord symbol library (it takes a couple of hours, but at least I get what I like, and I have loaded the library in all my templates), and, like you, I prefer to use ø. I thus have created that suffix, and I'm able to use it without any problem.
For your info, on my Azerty (French) keyboard, that symbol is available under opt-zero (opt is also alt on the Mac), but I have it in Maestro and you will have to find the correct slot for your set up.
If you cant' find the symbol in Broadway, you can create a chord suffix in which the ø is in another font (Maestro, etc...). Each element of a chord suffix can use a different font.
MacOsX 10.9.5, Mac Mini Intel Core i7 2,7 Ghz, 16 Go Ram, Dolet 6. Azerty kb. Full TGTools. MOTU Midi Express XT USB, Roland Sound Canvas SC-88vl, MOTU Audio Express.