Depending on the permissive license you plan on using, the question may be moot. In other words, if your code will have the basic freedoms that LGPL provides, then even a straight copy of the code is OK and the copyright holders are not likely to come after you.
Another point is that if the original code is GPL'ed then the author is not likely to be the type who is going to object to you deriving something from his algorithms and ideas (as copylefters tend to oppose software patents).
Usual IANAL disclaimers - I just don't think it's likely to be a real life problem unless you use substantial amounts of code and try to restrict the freedoms that the author intended to guarantee with their copyleft.
