So as promised a quick tutorial. What you need for this is a metal coat hanger (although metal piping or rod will do too), glue (I used the gw superglue), a saw/good knife and a guardsman (or if you have a valkyrie/vendetta one of the gunners is perfect).
So now onto how I did it.
You take your coat hanger and cut it to a rough size that you want. The you use this tool (not sure what it is refer to pics) in order to bend it (but I used my hands for most of it and then found that it made a better curve using the tool top picture red one) and make it more rope like. Since it's a metal coat hanger it should be magnetic (mine was) and since you magnetised your heavy bolters in side right? it should just pop on.
And that's it!