Haven't replaced bushes in a fork but I saw a bush removal tool for a Rockshox fork a while ago.
It was a metal disc the same diameter of inside of leg, with a piece cut off opposite edges to make it slightly narrower than diameter of bush so that it can pass through bush. The disc also has a slotted hole in it for long metal rod so disc can tilt as it passes through bush. The rod had a weight with hole down centre to act as a slide hammer on top end of rod.
Drop disc on rod down through bush, pull it up till it is flat under bush, then slide weight sharply upwards to remove bush.
If I was in your position I think I'd rather have a go making this tool from a bit of flat metal sheet and some screwed rod, nuts, washers and big socket to act as weight/hammer, than risk damaging inside of fork using screw-drivers or lengths of screwed rod to drift it out from below.
Edit to say I Googled this,
http://www.cheapbikeparts360.com/produc ... eal-tools/
not exactly as I remembered it though.
Have a look at page 15 here,
http://giant.kssina.com/Manage/Project/ ... 716944.pdf
It's for Rockshox but the method should be the same.