When a new window appears:
xtaskbaronadd !execute [!labelmoveby nodeusage $xtaskbarbuttonmaxwidth$ 0 $slidestep$ $slidetime$][!xtraymoveby $xtaskbarbuttonmaxwidth$ 0 $slidestep$ $slidetime$][!commandmoveby $xtaskbarbuttonmaxwidth$ 0 $slidestep$ $slidetime$][!labelmoveby TimeLabel $xtaskbarbuttonmaxwidth$ 0 $slidestep$ $slidetime$]

When a window is removed:
xtaskbaronremove !execute [!labelmoveby TimeLabel $-xtaskbarbuttonmaxwidth$ 0 $slidestep$ $slidetime$][!commandmoveby $-xtaskbarbuttonmaxwidth$ 0 $slidestep$ $slidetime$][!xtraymoveby $-xtaskbarbuttonmaxwidth$ 0 $slidestep$ $slidetime$][!labelmoveby nodeusage $-xtaskbarbuttonmaxwidth$ 0 $slidestep$ $slidetime$]

$slidestep$ and $slidetime$ are variables I created just before those two lines so that I can easily vary how fast it slides along.

When at item is added to the taskbar, "nodeusage" (fed from RSSreader for my internet usage) is slid first, then the xtray box, the lsxcommand box and then the time label.
When at item is removed, it's the opposite order - time, lsxcommand, xtray and then "nodeusage".

The loss of focus occurs AFTER the sliding has completed.