I believe you can be notified when a collection is imminent. I saw a service use that to remove instances from the load balancer before that happened - super useful for higher-percentile latencies.
I can almost make it work with some pretty aggressive hackarounds, such as subdividing my service into multiple, smaller processes that each operate w/ workstation GC mode. GC runs pretty fast when object count is reasonable. Something like 1 process per latency-sensitive client is where I am at with .NET right now.