Vivaspin with appropriate MW cutoff. This should separate the albumin from ur desired protein. 

I have found filter concentrators to be a pain and unreliable if the concentration of protein is vastly different. I would recommend using StrataClean resin from Agilent to concentrate your supernatants.

• 10 µL per 1 mL of supernatant.
• Rotate for 1 hour at 4C.
• Spin down, remove supernatant.
• Boil in minimal volume of 1X Laemmli buffer (50 µL should be good for 10 µL resin).
• Spin to settle resin before loading boiled sample on PAGE.

I use this technique to generate concentrated supernatants to probe for secreted proteins in the following paper:

Article K+ regulates Ca2+ to drive inflammasome signaling: Dynamic v...

If you wish to look at VEGF protein levels in large volumes of supernatant, you could use TCA precipitation.  You will precipitate all proteins, including albumin.  Protocol is available online.  

http://www.mic.ucla.edu/ms_pr/handouts/proteomics/protein_precipitation_protocols.pdf

Firstly, you can possibly try to reduce the % of FBS 24 hours after the electroporation. We've done it with a good preservation of cell viability for the WJ-MSCs, but with the TurboFect mediated transfection. And as most of the VEGF isoforms (with the exception of VEGF121) are binding to the heparin you can try to concentrate it on Heparin Sepharose beads (for the secreted VEGF you can simply add it to the cells in the process of cultivation).

Try Lipofection, instead of electroporation. Your cell viability will be better. For transient expression, you might not need for your cells to survive more than 48 hrs, post-transfection, unless of course when you need large amounts of protein. After about 6-8hrs following transfection, change the media to serum free DMEM-F12 (50-50). Cells do not thrive in this media, but can survive much better and express your protein. Life technologies (now thermo fisher) also sells reduced serum F12 media, that might just do the trick for you. For concentrating your protein, try using the Amicon® Ultra Centrifugal Filter tubes, from Millipore. You also might be able to cut-off BSA, if the size of your protein is significantly different from it, using these tubes. Good luck.

HLB columns form Oasis, Waters is an effective way of concentrating protein from supernatents, followed by lyophylization. The pure desalted protein thus obtained can be used to do Western blots.