I can refuse the offer, but I can't sell the novel to another publisher unless that publisher offers more than the best offer the first publisher makes. This is how it should be. Essentially, highest offer gets the novel, or no one does.
This is not the OP's question but I HAVE to say something. You've made this point before, and I still think you are wrong. Reputable agents are ALWAYS going to try to cut the "can't sell to another publisher unless that publisher offers more than the best offer the first publisher makes" bit.
Listen: If my client sells book 1 to Publisher A, and there is an option, fine. Publisher A will get the first crack at the new book. If they want to buy it, but they are not offering what we think it is worth, fine. We can either negotiate... or we can say NO. (Sometimes, gasp, people don't have that awesome an experience with a publisher, after all!) If WE want to work with Publisher A, we will negotiate and so will they, and we'll figure it out. If we DO NOT want to work with Publisher A... we say no, and are free to go anywhere else we want.
In YOUR scenario, Publisher A wants to publish. We DO NOT want to work with Publisher A. We say No Thanks, and shop it elsewhere. Publisher B seems much better for us, and we'd really like to switch. Maybe they are offering the same as PubA, but they are clearly better suited for the book. However, we have your ridiculous clause in the option, so we CAN'T say yes to PubB -- now we have to go back to PubA and discuss it with them? No. EFF publisher A. WE SAID NO TO THEM. We DO NOT want to work with them again. When you say no to them, they should stop being part of your business. This clause basically makes it so Pub A can hamstring a deal for you. ARGHHHHHH