It is most unlikely that he will now be able to do that.
The situation for him (driving a friend�s car) is no different to if he had been the registered keeper. I imagine that the keeper nominated him as the driver and that�s how he got his first letter (which he is going to say he never received). That original letter would have asked him to say who was driving, and if it was him, to say whether he wanted to accept the offer of a fixed penalty. He had 28 days to do that.
His opportunity to pay a fixed penalty for speeding has now lapsed and he is being summonsed for failing to provide details. The court will be unable to accept any payments in these circumstances. He will have to answer the Section 172 summons either by pleading guilty (which he may do by post or by appearing), or pleading not guilty (on the grounds that he did not receive then first letter). If he intends to plead not guilty he will have to appear.
The court will probe very carefully his claim that he did not receive the first letter. The onus will be upon him to convince the court that this is true, and he will be required to give evidence on oath. Furthermore, if he pleads not guilty but is subsequently convicted, he will obviously not be entitled to a discount on his fine (of up to one third) for a guilty plea, and he will be liable for considerably increased prosecution costs.
All in all, the terrible advice he received and acted upon is likely to cost him dearly.