Ok, I've found a solution that seems to work.
1. In the Model Explorer under Model Workspace, set data source to "MATLAB Code".
2. In the code box add something like:
hparam = find_system(get_param(bdroot, 'Handle'),...
'SearchDepth', 1, 'Name',...
'Name-Of-Parameter-Block');
VarName = eval(get(hparam, 'ParamName'));
3. In the Model Hierarchy of the Model Explorer, select your system, right-click and select properties.
4. Click the Callback tab and select InitFcn.
5. Add the following code:
hws = get_param(bdroot, 'modelworkspace');
hws.reload;
6. Close all dialogs and simulate a happy man/woman.
If you have a better solution please submit it.