Use SteamCMD or other tool to get the bin/dat file, edit the file with a text editor, notice how it contains 2 xml files, create a folder for the mod, within will be content.xml and a folder "md".
inside md will be the fbss.xml

content.xml:
<?xml version="1.0" encoding="iso-8859-1"?>
<content name="" description="" author="Assailer" version="108" save="false" date="2016-04-07" id="fbss" lastupdate="">
<text language="44" name="Fly-by Subscribe" description="Fly-by Subscribe" author="Assailer" version="1.08"/>
</content>

fbss.xml:

<?xml version="1.0" encoding="utf-8"?>
<mdscript name="fbss" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="md.xsd">
<cues>
<cue name="fbss_cue" instantiate="true" checkinterval="10s" namespace="this">
<conditions>
<check_value value="not player.zone.isclass.highway"/>
</conditions>
<actions>
<create_list name="$stations"/>
<find_station name="$stations" multiple="true" space="player.zone" known="true">
<match_distance object="player.primaryship" max="15km"/>
</find_station>
<do_all exact="$stations.count" counter="$si">
<set_value name="$station" exact="$stations.{$si}"/>
<do_if value="not $station.hastradesubscription and $station.relationto.{player.primaryship} ge 0.0">
<add_trade_subscription object="$station"/>
<set_known object="$station" known="true"/>
<show_help custom="'You have subscribed to ' + $station.name + '.'"/>
</do_if>
<do_if value="$station.hastradesubscription and $station.relationto.{player.primaryship} lt -5.0">
<remove_trade_subscription object="$station"/>
<show_help custom="'You have unsubscribed from ' + $station.name + '.'"/>
</do_if>
</do_all>
</actions>
</cue>
</cues>
</mdscript>