Question: obtain ProjectInstance in a right way

### Task
I have to obtain a `ProjectInstance` with build-time items and properties after build.
In case I have only one target framework everything is simple. But when I have several target frameworks defined by `TargetFrameworks` property it is not so easy because target `DispatchToInnerBuilds` performs build via other `ProjectInstance` objects.

### Current solution

So I have decided to emulate `DispatchToInnerBuilds` behavior:
```c#

void Build(Project originalProject, string[] targets)
{
var targetFrameworks = GetMultipleTargetFrameworks(originalProject);
if (targetFrameworks.Any())
{
foreach (var targetFramework in targetFrameworks)
{
// Specify TargetFramework
var actualProperties = new Dictionary(properties);
actualProperties["TargetFramework"] = targetFramework;

// Build project
var project = new Project(originalProject.Xml, actualProperties, null, _projectCollection, );
var projectInstance = _buildManager.GetProjectInstanceForBuild(project);
var buildRequestData = new BuildRequestData(projectInstance, targets, null, BuildRequestDataFlags.ProvideProjectStateAfterBuild);
var request = _buildManager.PendBuildRequest(buildRequestData);
request.ExecuteAsync(submission => { ... }, null);
}
}
else
{
...
}
}
```

After executing build in that way I have several `ProjectInstance` objects corresponding to project target frameworks.

### Problem
Usually it is ok, but I do not run outer build in that way. And this approach does not work with `NuGet.Build.Tasks.Pack.targets`.

There is a next target there:
```xml


```

And in my case I run builds only with `IsInnerBuild = true`.

### Possible solutions (as far as I can see)

1. Do not emulate `DispatchToInnerBuilds` and obtain `ProjectInstance` somehow. (how?)
2. Run outer build, but without invoking `DispatchToInnerBuilds` target. (how?)

Thanks for any suggestions. Maybe someone knows how to solve the issue in a **right** way...