This is perhaps not so easy to find in the documentation, but you can use the GET command (miscom.doc). You have to have your data in files with one item per line:
* reading data from file into vector
open unit 21 read form name x.dat
open unit 22 read form name y.dat

set i 1
label loop
get x@@i unit 21
if x@@i eq END-OF-FILE goto done
get y@@i unit 22
incr i by 1
goto loop
label done

set j 3
set k 5
write title unit 6
* @x1 @y1
* @x2 @y2
* @x@@j @y@@j
* @x@@k @y@@k

If you absolutely want to read several datapoints per line you can modify the code in source/charmm/miscom.src and recompile.

Good Luck!

Lennart Nilsson
Karolinska Institutet
Stockholm, Sweden