Hi heroicglaedr,
You can send HMRC a letter, outlining the expenses you wish to claim for each year.
If the expenses total is under £2500 in a year, we can process that claim through your regular PAYE record, without the need to file a return for that year.
Expenses claims over £2500 in a year will require a tax return for that year.
Please see guidance here:
Claim tax relief for your job expenses
Extra-Statutory Concessions
Thank you.