I happened to speak to my IFA yesterday and this came up. he explained that you have to use the current year's 40K allowance first. Then, if you wish to contribute more, you use (year-1)'s allowance, then (year-2)'s before you can use (yera-3)'s.
But I was just musing as the whether that scheme would actually accept them.
There needs to have been a scheme in place but you don't have to put your backdated pension into that scheme. I looked at putting my three years into my company scheme but they wanted 5%. Hargreaves Lansdown wanted 0%. No brainer.