[R] read.table input array

[Balpo]

  Hello to all!
I am new with R and I need your help.
I'm trying to read a file which contests are similar to this:
A    B    C    T    Lengths
1    4.0    0.0015258789    18    c(1,2,3)
1    1.0    0.0017166138    24    c(1,1,4)

So all the columns are numeric values, except Lengths, which is supposed to
be an variable length array of integers.
How can I make R read them as arrays of integers? Or otherwise, convert the
character array to an array of integers.
When I read the file, I do it like this
t1 = read.table(file=paste("./borrar.dat",sep=""), header=T, 
colClasses=c("numeric", "numeric", "numeric", "numeric", "array"))
But the 5th column is treated as an array of characters, and when trying 
to convert it to another class of data, I either
get two strings "c(1,2,3)" and "c(1,1,4)" or using a toRaw converter, I 
get the corresponding ASCII ¿? values.
Should the input be modified in order to be able to read it as an array 
of integers?

Thank you for your help.
Balpo