Format np.float64 without leading digits

I need to format np.float64 floating values without leading digits before the dot, for example -2.40366982307 as -.240366982307E+01, in python.
This is to allow me to write in RINEX 3.03 the values with 4X, 4D19.12 formats. I have tried f"{x:.12E}" but it always has a leading 1 for numbers greater than 1. I have also tried np.format_float_positional and np.format_float_scientific but those don't have restrictions on leading digits.

I would go for something custom designed from scratch. I agree, however, I did not think about all the marginal cases that can occur.

# Format a floating-point number to RINEX format
def format_rinex(value):
    if not np.isfinite(value):
        return f"{value}"

    sign = '-' if value < 0 else ' '
    abs_value = np.abs(value)
    exponent = 1 + np.int32(np.floor(np.log10(abs_value))).item() if value != 0 else 0
    mantissa = abs_value / (10 ** exponent)
    mantissa_str = f'{mantissa:.12f}'.replace("0.", ".")
    return f'{sign}{mantissa_str}E{exponent:+03d}'

Formats your example number into -.240366982307E+01.