The only way I can think of is rather drastic. I would require you to restore your iPad using the iPhone's backup. This would affect everything on the iPad, and is probably too messy for what you'll get in return. Often, you have to re-enter passwords after doing this anyway, so it could easily turn out to be a lot of trouble for nothing.
Most websites have password recovery options when you visit them. Failing that you should be able to contact the provider directly to verify who you are and get the password reset. This would be the better route if available.