PTA to solve this unconventionally, using a way of collecting preferences from those who can't be present (6,4)
I believe the answer is:
postal vote
'a way of collecting preferences from those who can't be present' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'pta to solve this unconventionally' is the wordplay.
'this unconventionally' indicates anagramming the letters.
'pta'+'to'+'solve'='ptatosolve'
'ptatosolve' with letters rearranged gives 'POSTAL VOTE'.
'using' is the link.
Can you help me to learn more?
(Another definition for postal vote that I've seen is " Arrangement for absent elector".)