Underpaid 401k over the year. Can I throw a bunch of post-tax money into 401k? Will it count as pre-tax money instead?

My 401k match was .. way under what it should have been over the year. I have a bunch of money in savings. Is there a way to put money from that savings’ account into my 401k and then take that money off my taxable income as pre-tax 401k funds? Or, would all ways that I put money into the 401 be the post-tax 401k version because it didn’t happen at time of pay check?