yeah,, they do make splice kits for plastic. You will probably find that using the plumbers glue will also make a better connection. the glue will fuse the plastic insert to the line by that magical chemical process.
Im my opinion,, id put an outter sleeve on vs an insert.,,why? an insert would probably cause a fuel flow restriction(decreasing the inner diameter of the line.
if you can find an outter sleeve of some sorts,,put the glue on the outside of your line and slip the sleeve on each loose end.
even better would be if you could heat up the line and slide an insert large enough up inside each end but id be skitish on that cause your dealing with gas.