How to keep both keys after join with a named "by" in R

Question

With the dplyr join functions, you can use a named by if the join variables have different names. But the documentation warns "Note that only the key from the LHS is kept". How can I keep both keys?

eg

library(dplyr)
df1 <- data.frame(name= c("Ann", "Betsy", "Charlie", "Dave"), 
  dob= c(as.Date("2000-01-01", "%Y-%m-%d"), 
        as.Date("2001-01-01", "%Y-%m-%d"), 
    as.Date("2002-01-01", "%Y-%m-%d"), as.Date("2003-01-01", "%Y-%m-%d")),
         stringsAsFactors=FALSE)

df2 <- data.frame(name= c("Ann", "Charlie", "Elmer", "Fred"), 
      date_birth= c(as.Date("2000-01-01", "%Y-%m-%d"), 
        as.Date("2004-01-01", "%Y-%m-%d"), 
        as.Date("2001-01-01", "%Y-%m-%d"),
as.Date("2006-01-01", "%Y-%m-%d")), stringsAsFactors=FALSE)

Joining:

 inner_join(df1, df2, by = c("name","dob" = "date_birth"))

     #  name    dob
     #  Ann     2000-01-01

How do I keep the dob and date_birth columns?