1. The A pillar trim is held on by clips in the bodywork/pillars themselves which are very tight so you have to be gentle but firm (contradictory perhaps) and the trim will eventually 'pop' off
2. The wire can be fed from the back of the radio and guided up the A-pillar trim but it will probably help if you tape it to something rigid like an unwound wire coat hanger so as to be able to see it and feed it through the gaps.