What is the best work flow, to convert the anamorphic material in premiere?

[Valla]

I have a lot of material shot in anamorphic but its a pain in the $#% to strech every single clip..

[Tim McC]

You could transform the first clip, copy it, then paste attributes on all the other clips after selecting them all.  (You want to do this first, before color correcting or any other adjustments.)

[slvs]

Use the Motion effect (should always be there) under your Effects Control tab, uncheck the box next to Uniform Scale and then rescale the height, this effect will also be transferred via Paste Attributes.