i know the 300 ohm twin lead is hard to work with, but give it your best
shot.
The reason being that the twin lead keeps the pair of wires an exact
distance apart over a long length.  This is vitally important to the j poll
design.  If you can make some exact spacers and make sure the copper wire
your using is perfectly straight and without kinks, then you might be able
to make a j poll with just straight copper wire.
300 ohm twin lead is such that the wires are also the perfect distance apart
for a particular j poll design.
If you alter this spacing, you'll end up with allot of headache, even more
then working with the twin lead.
I found a very new utility knife works quite well with the plastic of the
300 ohm twin lead...a bit tricky to to strip it sometimes, but once you
experiment on a spare piece, you'll get the hang of it.
73
Colin, V A6BKX