suppress messages displayed by "print" instead of "message" or "warning" in R

Many R packages I work with involve functions that give all their messages and warnings through commands to print() calls rather than commands to message() or warning(). I'd like to be able to silence these functions progress indicators, etc, but the standard supressWarnings() or supressMessages doesn't do it. Is there a way I can just suppressPrint?

For example:

silly_developer_function <- function(x){
   print("Thanks for using my function!!")
   if(is(x, "numeric"))
     print("warning, x should be a character")
   x
}

I'd like to have a simple function suppressPrint() that I could wrap around a call to this function that would suppress the warning and useless messages (but still print the return value).