Ayatollah Hadavi Tehrani’s answer is as follows:
1. It is permissible to perform ruku immediately after recitation; there is no need to say the recommended dhikr, although of course it is mustahab.
2. What is meant by the qiyam connected to ruku’ is to go to ruku’ from qiyam (the standing position). Therefore if someone accidentally goes down to sajdah but remembers s/he has not performed ruku’ yet before reaching sajdah, s/he must stand up straight and then do ruku’ and abstain from going to ruku’ straight from the bended position s/he was previously in.