I would say that it's too late to do it via a broker although the market is still quoting a price for the nil rights.
If you are in the UK, and you don't have a broker, I don't think you could do it in time.
As of this evening the rights were worth around 19 cents each. All other things being equal, this is what they will be worth next Tuesday.
If the BoI share price is 75 cents next Tuesday, people will want to buy the rights for 20 cents, so I would imagine that is what you will get. If there are huge volumes of rights for sale that day, it might artificially depress the market, so you might get less than you would get by selling them now.
But I don't think you can do anything about it now.
Note: I am a rights holder and intend to subscribe for the shares