Proper tools make all the difference. Your method works best on steel sights.
If this is your only Glock-- pay the armorer $20 to put it in for you-- easiest, cheapest solution. If you buy the nightsights from them, sometimes they install for free.
If you have multiple glocks, then invest the tools. ~$80 for the rear pusher ~$15 for the front staker or wrench. The advantage of owning your tools is that you can drift your rear sight if needed.