When using postscribe as tag-writer, you're most likely creating a dependency in your document-head. lazy-postscribe is a lightweight dependency, which can be included in your non-blocking js-loader-bundle.
Instead of calling postscribe directly, use:
lp.l(element, html, options);
Add the callback to your js-loader (e.g. nbl):
nbl.l(['postscribe.js', function() {
lp.c();
}]);
You may also add a second tag-writer, which will be executed after postscribe finished it's work:
lp.a(function() {
window.tagWriterFunction();
});