You could use Hashmask or Halfmask, they hide or "encode" the password on the client side. The only downside is most users will be unfamiliar as to what each is doing.
Actually you can do this with HTML+JavaScript. It would require either...
1. An editable iframe in place of the password box.
2. An "invisible" password input box with a dynamic changing element behind it representing the password input.
3. A password box with transparent text and a dynamically changing background representing the password input.
While it is possible I would not recommend that you pursue it, because you will probably only confuse your users in the end.