There are a number of ways inputting pinyin with tone. Beside Mimi's method, I can input tone marks with my Chinese inputting application (QQ Pinyin Input Method - QQ拼音输入法）.
The simplest way: QQ Input provides a feature of '开启v模式 - v mode'. When selected, you can input tone marks by typing 'v8' (a opcode) , i.e. āáǎà. However, the setting menu is in Chinese, if you can't understand, you can add my Wechat: nicedayjohn for instruction.
An alternative way is pre-input all vowels into a word file, and copy them when you need.
Some input tools (Such as QQ pinyin) can provide an on-screen keyboard by which you can input vowels. However this is a bit complicated and not recommended.