想了个办法绕过这个问题：自己写正则表达式检查文本中是否有需要每位数字单独合成语音的连续数字，如果有就转成中文数字，再调用插件合成语音。以下以检测并转换国内固定电话号码为例：

const plugin = requirePlugin('WechatSI');
function textToSpeech(content) {
	const digitsToChinese = (digits) => {
		if (!/^[0-9]+$/.test(digits)) {
			throw new Error('请输入一个自然数');
		}
		const chineseChars = ['〇','一','二','三','四','五','六','七','八','九','十'];
		let retVal = "";
		for (let digit of digits)
			retVal += chineseChars[digit];
		return retVal;
	}
	// 国内固定电话的正则表达式
	const DIGIT_REGEP_PHONE = /(?:[\(（]?0\d{2,4}[\)）]?-)?([2-9]\d{5,7})/g;
	let matched;
	while ((matched = DIGIT_REGEP_PHONE.exec(content)) != null) {
		const chinese = digitsToChinese(matched[1]);
		matched[1] = matched[0].replace(matched[1], chinese);
		content = content.replace(matched[0], matched[1]);
	}


	plugin.textToSpeech({
		lang: "zh_CN",
		tts: true,
		content,
		success: (res) => {
			if (res.retcode == 0) {
				console.log("合成的语音文件Url: " + res.filename)
			} else {
				console.error("无法合成语音：未知错误");
			}
		},
		fail: (err) => {
			console.error("Error on TextToSpeech: " + JSON.stringify(err));
		}
	});
}