SignalTap & Keep Attribute - how to prepare signals for SignalTap during RTL coding?

Unfortunately, this is not entirely true as it seems. Nodes that get removed in synthesis cannot be selected in SignalTap using pre-synthesis. The signals are visible when using the option "Design Entry (all names)", but attaching SignalTap to registers that get optimized away is not possible. Neither the syn_keep attribute and the preserve attributes work. The only way to get SignalTap to attach to these registers is to combine them with a dummy logic function that is never true, and then or it to some other signal that is used. :-(