Half Subcarrier spacing in LTE Uplink
For implementing the frequency shift of 7.5 kHz you will have to apply oversampling at some point in your system. There are two principal methods to achieve this: in frequency domain or in time domain.

Frequency domain

You could simply apply an additional zero padding in frequency domain by using a 2048 IFFT and by setting every second subcarrier to zero. You then shift all subcarriers by one frequency bin to achieve the frequency shift. This will maintain the frequency spacing of 15 kHz but the bandwidth of each subcarrier will be divided by two compared to the 1024 IFFT.

Time domain

You apply two-times oversampling to the time domain signal at the output of the IFFT. This can be done by padding a zero sample after each sample followed by a lowpass filter or some other interpolation method. The frequency shift can then be achieved by multiplying the resulting signal by $\exp(j\Omega_1 n)$, where $\Omega_1$ is the 7.5 kHz normalized to the new sampling frequency (double the original sampling frequency) and $n$ is the discrete time.

Which method to choose depends on how close your simulation should be to the hardware implemenation. If the system you model has some intermediate frequency oscillator to do the frequency shift, the time domain method can model this. But if your digital-to-analog converter is fast enough and if you can implement a 2048-IFFT at the required speed, this is probably the way to go and you should therefore model it accordingly.