Just reducing/removing the alligence penalties across the board is the only thing you could do.
Which file do I need to do that?
The Gameplay.Constants file in the Gameinfo folder. Find this section.
planetBaseAllegianceAtDistanceCount 11
allegiance 1.00
allegiance 0.90
allegiance 0.80
allegiance 0.70
allegiance 0.55
allegiance 0.40
allegiance 0.25
allegiance 0.25
allegiance 0.25
allegiance 0.25
allegiance 0.25
Where the first allegiance is your homeworld, the second is one is one jump away, the third is two jumps away etc. Change them all to 1.00 for example and every planet will have 100% base allegiance like your homeworld.