A crimped connection – bugga. The best way would be to remove the PL-259 connector at the radio end (which should be a solder type or can be replaced with one), and then re-route the cable from the new antenna mounting position.
PL-259 connectors are pretty easy to fit, lots are just crimped these days and no soldering required.
Any join in the cable introduces some amount of loss, so better to have one continuous length where possible. If you have any cable left over, rather than coil it up, chop it out. The longer the cable the more loss.
For joining...
If you're handy with a small soldering iron and fiddly bits, then Jaycar should have a pair of BNC connectors – 1 x male and 1 x female (to suit RG-58 coax cable), and fit them about 150mm from the antenna base. The parts would cost about $10 or less, and maybe half an hour to fit. Crimp type are cheaper and faster, but you'd also need the correct crimp tool for the job.
This pdf link shows how to fit the male connector...
http://www.solidsealing.com/technica...ts/ns10551.pdf
Otherwise a quote from a radio shop or competent hobbiest to fit them might be easier.