A way to evaluate expression/call function, on demand, while the app either running or on break mode

I'm writing a VS extension that would allow me to change data/get data from a debuggee, and to call some of it's functions. All of it is required to be able to run while it's in break mode or running. I tried to use expression evaluator, but it crashes the app when it's doing something (call stack becoming corrupted, there are 0xffffff's return addresses appearing there), and only works as desired while app is in break mode. I tried to create remote threads, but by some reason they don't work as well. It seems like there should be some universal solution for both cases, like "enter the break mode, evaluate expressions, exit the break mode" but using  EnvDTE90a::Debugger4::Break doesn't do much too, it just hangs until i stop the app from IDE window. All of it seem pretty weird and indicate that's i'm doing something wrong. Any advice?