I guess I don't understand the problem or maybe I don't understand exactly what you are trying to to do.
I simply click on an item (or lasso all the items in a track or tracks) then drag it over to where I want it. Snap to Grid can be on or off.
I suppose if I ran into a problem where the program only renders from the beginning of the item I would insert a new track, move the vertical cursor line to the far left and record silence for a few bars. Then set my vertical cursor line to where I want to start rendering from. Could also record silence at the end of the silent track.
When rendering Reaper has options including Custom Time Range so having extra dead time at the beginning and/or end isn't a problem. My multi track projects always have more time than needed. After I render it down to stereo I open the stereo track in Reaper and edit beginning and end then render again.
Does this make sense or did I completely miss the point?

Does the noise in your head bother me ?