BootHID has a 1k boot size and is USB HID compatible so no drivers are needed.
Use [url=http://www.obdev.at/products/vusb/bootloadhid.html]BootloadHID.exe[/url] or [url=http://vusb.wikidot.com/project:hidbootflash]HIDBootFlash[/url] to flash firmware.

Compiling BootHID requires WinAVR/AVR Toolchain and an ISP to burn the bootloader.
Guide to setup WinAVR/AVR Toolchain.
Guide to using Teensy 2/Pro Micro as an ISP.

[b]Compiling BootHID bootloader and flashing to Pro Micro (on Windows)[/b]

http://deskthority.net/workshop-f7/bootloaders-t7608.html#p154660
1) Decode the link for BootHID v02, download and extract.

2) Navigate to '<where you extracted BootHID-02.zip>\BootHID\default\' and edit 'makefile'.

Configuring BootHID for Pro Micro clone

Change
[code]INCLUDES = -I"C:\Data\Teensy\AVR\BootHID\..\includes"[/code]
To
[code]INCLUDES = -I"..\..\includes"[/code]

3) Compiling

 3a) Open a command line window.  Start Menu > Run > type cmd.exe in the box.

 3b) Navigate to '<where you extracted BootHID-02.zip>\BootHID\default\'
 example of what you type in the cmd window:
[code]<drive-letter where it's extracted>:
CD '<where you extracted BootHID-02.zip>\BootHID\default\'
[/code]

3c) 'make clean' then 'make' (It's good to get into the habit of running 'make clean' before 'make')

3d) If everything compiled correctly with no errors, 'BootHID.hex' is the bootloader you seek.

4) Configuring the Pro Micro clone's fuses and burning the bootloader

The blue Pro Micro clone has default fuses of lfuse:FF, hfuse:D8, efuse:CB.

Entering those in the [url=http://eleccelerator.com/fusecalc/fusecalc.php?chip=atmega32u4&LOW=FF&HIGH=D8&EXTENDED=CB&LOCKBIT=FF]eleccelerator.com fuse calculator[/url].

Here we see 'Boot Flash size=2048 words' in the dropdown box under High fuse presets.  2048 words = 4096 bytes, i.e. 4k (of 32k total flash on 32u4) is reserved for the bootloader.  We want to change it 'Boot Flash size=512 words' because BootHID only needs 1k bytes.  Doing that will change hfuse to 'DC', but we're not done yet.  We also want to uncheck 'Boot Reset vector Enabled' under High fuse presets, this will change hfuse to 'DD'.