update.formula has 512 char buffer?

Hello,

I am trying to "paste" together a formula to use in the mob function of
party. This means the formula will be of the form y ~ x1+ ...+xM | z1+..zN.

I am doing some preliminary fits of y ~ x1+ ...+xM, then want to add the
conditional part of the equation using update().

Here's the test code:
var1 <- 1:78
x1 <- paste("x", var1, sep="")
f1 <- paste("f", var1[1:10], sep="")

# use first 77 variables
fmla <- as.formula( paste("y ~ ", paste(x1[1:77], collapse=" + ", sep=""),
sep=""))
fmla2 <- update(fmla, paste(". ~ . | ", paste(f1, collapse= " + "), sep=""))

# CHANGE x to all 78 variables
fmla <- as.formula( paste("y ~ ", paste(x1, collapse=" + ", sep=""),
sep=""))
fmla2 <- update(fmla, paste(". ~ . | ", paste(f1, collapse= " + "), sep=""))

I have run this in Windows and Linux (64 bit) and both fail when using all
78 terms (and anything more than 78 terms). The error message contains
Error in parse(text = x) : :1:514: unexpected ')'.

Changing the length of the names of the x variables will break the update()
with fewer variables, but always with an error referring to just more than
512 characters. ?There is nothing special about 77 or 78 variables here; I
want to do this with hundreds of variables.

Is there a workaround to this?

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