GoArrow wasn't designed to let you do this, but if you really want to, you can "hack" the settings file to make it load a route you want.
Basically, any time you want to load a custom route, you'd need to log out, modify your settings file, then log back in. In the settings file, find the <arrowTarget> node and replace its contents with:
<arrowTarget>
<route routeIndex="0" distance="0">
<loc id="-1" name="First Location" type="Custom" NS="51.2" EW="-42.5" />
<loc id="-1" name="Second Location" type="Custom" NS="50.8" EW="-45.1" />
<loc id="-1" name="Third Location" type="Custom" NS="52.4" EW="-48.7" />
<loc id="-1" name="Fourth Location" type="Custom" NS="52.0" EW="-41.5" />
<!-- etc... -->
</route>
</arrowTarget>
A few notes: all the locations should have id="-1". For NS: north is positive, south is negative; for EW: east is positive, west is negative. I don't have an AC subscription, so I can't test to see if this works. Let me know if you have any trouble with it.
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[LotRO] Digero (Guardian), Digrim (Burglar), Dignite (LM), Azrea (Hunter) - Landroval
[AC] Digero, Lyera, Draxxe - Leafcull (Retired)
[CoH] Devil's Zealot, Scinta, Izzard - Guardian (Retired)
Digero's AC Decal Plugins:
http://decal.acasylum.com