demo.s

.global _start

.section .text
_start:
    # Setup stack frame
    movq %rsp, %rbp

    # Load argc
    movq (%rbp), %r8       # %r8 now holds argc

    # Load argv
    leaq 8(%rbp), %r9      # %r9 now points to argv[0]

    # Find envp by iterating through argv until NULL is found
    movq %r9, %r10         # %r10 will be used to find envp
find_envp:
    movq (%r10), %rdi      # Load the current pointer in argv
    cmpq $0, %rdi          # Compare it to NULL
    je envp_found          # If NULL, we've found the end of argv
    addq $8, %r10          # Otherwise, move to the next pointer in argv
    jmp find_envp

envp_found:
    addq $8, %r10          # Move one more step to point to the start of envp

    # Allocate space on the stack for the new argv array
    subq $8, %rsp          # Space for NULL termination
    subq %r8, %rsp
    subq %r8, %rsp         # Space for argc pointers (including argv[0])
    movq %rsp, %r11        # %r11 now points to the start of the new argv array

    # Copy argv pointers to the new array
    movq $0, %rcx          # Counter
copy_loop:
    cmpq %rcx, %r8
    je copy_done
    movq (%r9, %rcx, 8), %rdi
    movq %rdi, (%r11, %rcx, 8)
    incq %rcx
    jmp copy_loop

copy_done:
    movq $0, (%r11, %rcx, 8)   # NULL-terminate the new argv array

    # Check if argc > 0
    cmpq $0, %r8
    jle .Lexit

    # Execute execve syscall
    movq $59, %rax          # syscall number for execve
    movq (%r11), %rdi        # filename is argv[0]
    movq %r11, %rsi         # New argv array
    movq %r10, %rdx         # envp
    syscall

.Lexit:
    # Exit the program using the exit syscall
    movq $60, %rax
    xorq %rdi, %rdi
    syscall

Quite cool! You can nonetheless speed up the whole thing by jumping directly to environment which is basically &argv[argc + 1] (you can test in C code if you want to be sure about it).
I would say something like this should do the trick but I am not an expert in amd64 assembly (or assembly at all):

movq r9, r11
add $1, r11 # r11 is argc + 1
movq (%r9, %r11, 8), r10 # r10 is &argv[argc + 1], i.e. environment