It's definitely the most fun idea, but it's somewhat fragile and subject to the whims of my internet connection. Also not feasible to permanently tie up an entire account to do this. I guess I didn't specify in the OP, but this is for the purpose of a rune library, so it would need to be a solution that's always accessible.
I would just place a small tower up in front and bridge them. Use the small tower as the entry point to the roof and subsequently the rest of the fort. You bypass the main doors and you keep the CY secure. (Obviously, only if you have the room)
There's an way to gain access to the other areas of the fortress but it involves an exploit. Anyone that has played on Angel Island might have an idea of how this works, and I have no doubt that Telamon would ban someone for pulling it off.
You could always hire somebody to dedicate an account to it. They will get paid in Plat (so long as the Telacare system is in place). hahaha. But I think that's the best solution I can come up with. I tried for a while to make other things work, but it seems to no avail...
The tower wings are the only way to get over that 1 tile gap which is the minimum between 2 placed houses. This is because the wing overhangs that gap.
Wouldn't players be able to enter through steps in the hallway when polymorphed into, say, a chicken?
I have few rules in life, but one of them is: when someone's first post involves "polymorphed into, say, a chicken", I expect big things from them. Player heights are still 16z even when polymorphed into a chicken or a slime, as far as I can tell.