[R] Applying do.call to a data.frame using function arguments

[miller_2555]

I'm trying to convert a data.frame to a series of strings (row-wise). There
was a very good discussion awhile back (2002) entitled "[R] string
concatenate across rows of a matrix??" where Tony Plate recommended the
following two alternatives (x2 is an R object of type data frame -- a matrix
also works for solution #1): 
    1) apply(format(x2), 1, paste, collapse=" ");
    2) do.call("paste",x2)

I applied each solution to a 1000x7 data frame, and found the do.call
function takes <75% of the average time taken by the apply function on my
particular system (repeated the comparison a few thousand times). I would
like to use the do.call option for the x2 data frame for the increased
performance, but cannot determine how I can also feed arguments to the paste
function (specifically, I am trying to create comma-delimited values instead
of space-delimited with each value wrapped in quotes). For instance:
x2 <- as.data.frame(rbind(c(1,2,3),c(4,5,6))); => 
[1] " 1\",\"2\",\"3 "
[2] " 4\",\"5\",\"6 "

This result is obtained via the following command:
apply(format(x2),1,paste,collapse='","',sep=''); =>
               1               2 
"1\",\"2\",\"3" "4\",\"5\",\"6" 

However, I cannot obtain the same result using do.call. The best I have
managed is the following code:
do.call("paste",list(what=x2,collapse=',')); 

Unfortunately, the list function appears to mangle the data.frame w/r/t the
do.call function. Is anyone aware of the appropriate call (or other
optimized function that runs at least as fast as the do.call function)? 


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