Using the OU to supplement other studies.

I'm currently studying Economics at a bricks and mortar uni. The course I'm studying, being a BA and not a BSc, doesn't have as much mathematics as I was expecting. I was thinking I might remedy this by signing up for the Certificate of higher education in maths at the OU and studying one unit at a time. I feel that I have enough time to study and obviously I can use my own uni's library and facilities. Assuming I can afford the fees what are peoples opinions on this? possible? too much?

Any help would be great.

Completely doable, and if you can do it part-time and finish it at the same time you finish at your brick university, completely ideal.