Thanks Vgeri,
I was initially planning to arrange reference from my colleague in the current company, defnitely not line manager. However, my colleague, whom I had been constantly updating about my MBA plans, had to go on emergency vacation due to a personal emergency and he won't be back before the R2 deadlines

Sadly, he won't be able to access internet during this duration.
Hence, I started thinking of other alternative. Additionally, I had previously asked my former colleagues to provide me references and they know me a lot better and could back up my start-up experiences with anecdotes. My current company is a consulting firm. Not sure if I should wait for my current colleague to be back sooner or approach my former colleague. Should I ask LBS about this?

Agreed with vgeri on this -- you can use previous colleagues/managers for both recommendations, but not having a current employer reference can potentially be a disadvantage. Generally, what I've seen is when previous employers are used, the reasons for not using current employer recommendations are explained in the optional essay. If you have not been with your current employer for long (less than a year, for example), that's another reason that is often explained in the optional essay.