There is a trick that may work for some pieces but requires very careful setup:
- create a new database that can be part of the MIRROR
- then you can map the components that are INDEPENDENT of the local instance to this DB

Be warned:
Identification and Isolation of these pieces can be quite tricky and sometimes also impossible
In addition, this can make troubleshooting and maintenance (release update?) rather complicated
and you should do an in-depth evaluation if the extra effort values the achieved result.  

@Alexey Maslov
I had a similar experience with "InPlace".
This may work if your applications are as simple as in SAMPLES:
[ "nome est omen" SAMPLES => Simple]
Just a few $ZU() or other %z* stuff may break you, or file references containing *CACHE*.
Or some $ZF() functions with c-binding, ....

Therefore I designed my "2 worlds" approach using ECP as a data bridge: 
Using ECP across IRIS and Caché