Actually it looks like you can do it with the help of a Spannable:
String text = "This is an example";
Spannable s = new SpannableString(text + " text");
s.setSpan(new TypefaceSpan("monospace"), 0, text.length(),
Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
s.setSpan(new TypefaceSpan("serif"), text.length(), s.length(),
Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
((TextView)findViewById(R.id.my_text_view)).setText(s);
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