Yes General .5 is on a pk at -105 and .5 is +.5 at -105. But no you can not defer either half. Normally Pinnacle will let you pick your line with the use of a drop down menu, i.e. (pk, pk & +.5, or +.5), all with differnet payouts of course. But they don't get as much action on FA cup games so they don't bother.
If you like the Pinny line but only want half of it you could offset the half you don't want at another book. But then of course you could have bet the half you did want at that book as well.