I tried several times to switch my budgies over to pellets...and tried every approach suggested. None worked...so I figured that a slightly less healthy but happy budgie is better than a stressed out, hungry or dead one.
So, they eat seeds and get leafy greens because that is about all they'll eat. Mind you, the stray budgie I found about 7 years ago is probably in his early teens by now so the all seed diet can't be THAT horrible for budgies.
All you can do is your best....