Hey IK,
Just because someone is vegetarian doesn't mean they can't do LCHF/ Keto. If you were thinking along those lines it's totally possible. If he was vegan he would have to cut conventionally. But avocados, nuts, eggs, whey, cottage cheese, coconut, ect. It's all still on the table.
But it sounds like you are asking more along the lines of chemical help. GW works better with carbs than Clen, so it might be a good choice. The actual mechanism and reason for fat-loss between the two is different though (although you know that) so training will be adjusted.
Otherwise, some might stone me for this, but T3 is also an option (of course combined with an anabolic and possible an additional fat burner).
Will using Clen for 4 weeks help? Yes, but it's not going to negate a bad diet. Not saying his diet is bad, but his training should make him sweat like a hambeast. I have not read one anecdote of a vegetarian using Clen.
Hope it makes sense and helps a bit.
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