There is a workaround here, but it’s definitely not ideal:
I opened a topic on the Ember forum about it, but it doesn’t seem like there is any clean way to allow all params:
The workaround suggested there could potentially work if you know the parameter names up-front.
It could be interesting to experiment with a theme component which takes a list of query param names (e.g. gtm_source), and modifies controller:application to include them. 